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 $236.42   12.211%   $265.2892   $265.29   $265.30   $265.30  
  Purchase #2 $139.83   4.503%   $146.1265   $146.13   $146.15   $146.10  
  Purchase #3 $39.77   9.635%   $43.6018   $43.60   $43.60   $43.60  
  Purchase #4 $96.30   12.772%   $108.5994   $108.60   $108.60   $108.60  
  Purchase #5 $94.80   13.515%   $107.6122   $107.61   $107.60   $107.60  
  Purchase #6 $181.61   10.340%   $200.3885   $200.39   $200.40   $200.40  
  Purchase #7 $226.35   8.493%   $245.5739   $245.57   $245.55   $245.60  
  7 purchase totals = $1,015.08       $1,117.1915   $1,117.19   $1,117.20   $1,117.20