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 $108.72   9.432%   $118.9745   $118.97   $118.95   $119.00  
  Purchase #2 $6.80   6.831%   $7.2645   $7.26   $7.25   $7.30  
  Purchase #3 $250.33   7.690%   $269.5804   $269.58   $269.60   $269.60  
  Purchase #4 $214.97   10.346%   $237.2108   $237.21   $237.20   $237.20  
  Purchase #5 $230.77   7.731%   $248.6108   $248.61   $248.60   $248.60  
  Purchase #6 $24.70   11.716%   $27.5939   $27.59   $27.60   $27.60  
  Purchase #7 $198.99   6.275%   $211.4766   $211.48   $211.50   $211.50  
  7 purchase totals = $1,035.28       $1,120.7115   $1,120.70   $1,120.70   $1,120.80