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 $6.53   6.533%   $6.9566   $6.96   $6.95   $7.00  
  Purchase #2 $32.65   5.694%   $34.5091   $34.51   $34.50   $34.50  
  Purchase #3 $227.97   8.674%   $247.7441   $247.74   $247.75   $247.70  
  Purchase #4 $60.76   6.354%   $64.6207   $64.62   $64.60   $64.60  
  Purchase #5 $210.68   8.736%   $229.085   $229.09   $229.10   $229.10  
  Purchase #6 $224.60   8.601%   $243.9178   $243.92   $243.90   $243.90  
  Purchase #7 $98.35   6.383%   $104.6277   $104.63   $104.65   $104.60  
  7 purchase totals = $861.54       $931.4610   $931.47   $931.45   $931.40