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 $197.63   6.349%   $210.1775   $210.18   $210.20   $210.20  
  Purchase #2 $250.42   4.209%   $260.9602   $260.96   $260.95   $261.00  
  Purchase #3 $76.92   11.204%   $85.5381   $85.54   $85.55   $85.50  
  Purchase #4 $237.35   9.529%   $259.9671   $259.97   $259.95   $260.00  
  Purchase #5 $200.82   6.209%   $213.2889   $213.29   $213.30   $213.30  
  Purchase #6 $236.37   10.132%   $260.319   $260.32   $260.30   $260.30  
  Purchase #7 $47.68   11.821%   $53.3163   $53.32   $53.30   $53.30  
  7 purchase totals = $1,247.19       $1,343.5671   $1,343.58   $1,343.55   $1,343.60