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 $112.74   11.288%   $125.4661   $125.47   $125.45   $125.50  
  Purchase #2 $112.25   6.763%   $119.8415   $119.84   $119.85   $119.80  
  Purchase #3 $203.47   10.389%   $224.6085   $224.61   $224.60   $224.60  
  Purchase #4 $169.80   11.526%   $189.3711   $189.37   $189.35   $189.40  
  Purchase #5 $53.75   8.664%   $58.4069   $58.41   $58.40   $58.40  
  Purchase #6 $234.75   10.828%   $260.1687   $260.17   $260.15   $260.20  
  Purchase #7 $154.68   10.832%   $171.4349   $171.43   $171.45   $171.40  
  7 purchase totals = $1,041.44       $1,149.2977   $1,149.30   $1,149.25   $1,149.30