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 $89.97   8.177%   $97.3268   $97.33   $97.35   $97.30  
  Purchase #2 $213.27   10.170%   $234.9596   $234.96   $234.95   $235.00  
  Purchase #3 $28.94   11.848%   $32.3688   $32.37   $32.35   $32.40  
  Purchase #4 $68.96   10.707%   $76.3435   $76.34   $76.35   $76.30  
  Purchase #5 $83.94   10.823%   $93.0248   $93.02   $93.00   $93.00  
  Purchase #6 $117.78   10.514%   $130.1634   $130.16   $130.15   $130.20  
  Purchase #7 $193.54   4.537%   $202.3209   $202.32   $202.30   $202.30  
  7 purchase totals = $796.40       $866.5078   $866.50   $866.45   $866.50