Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $96.61   10.837%   $107.0796   $107.08   $107.10   $107.10  
  Purchase #2 $241.88   12.361%   $271.7788   $271.78   $271.80   $271.80  
  Purchase #3 $112.60   12.780%   $126.9903   $126.99   $127.00   $127.00  
  Purchase #4 $164.57   11.558%   $183.591   $183.59   $183.60   $183.60  
  Purchase #5 $203.90   5.368%   $214.8454   $214.85   $214.85   $214.80  
  Purchase #6 $118.64   10.120%   $130.6464   $130.65   $130.65   $130.60  
  Purchase #7 $194.91   6.124%   $206.8463   $206.85   $206.85   $206.80  
  7 purchase totals = $1,133.11       $1,241.7778   $1,241.79   $1,241.85   $1,241.70