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 $55.58   11.587%   $62.0201   $62.02   $62.00   $62.00  
  Purchase #2 $17.53   7.288%   $18.8076   $18.81   $18.80   $18.80  
  Purchase #3 $249.27   4.428%   $260.3077   $260.31   $260.30   $260.30  
  Purchase #4 $96.63   11.844%   $108.0749   $108.07   $108.05   $108.10  
  Purchase #5 $108.37   8.216%   $117.2737   $117.27   $117.25   $117.30  
  Purchase #6 $233.86   13.578%   $265.6135   $265.61   $265.60   $265.60  
  Purchase #7 $243.61   11.323%   $271.194   $271.19   $271.20   $271.20  
  7 purchase totals = $1,004.85       $1,103.2915   $1,103.28   $1,103.20   $1,103.30