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 $59.64   6.859%   $63.7307   $63.73   $63.75   $63.70  
  Purchase #2 $245.39   4.419%   $256.2338   $256.23   $256.25   $256.20  
  Purchase #3 $244.75   6.369%   $260.3381   $260.34   $260.35   $260.30  
  Purchase #4 $229.75   13.219%   $260.1207   $260.12   $260.10   $260.10  
  Purchase #5 $110.48   9.221%   $120.6674   $120.67   $120.65   $120.70  
  Purchase #6 $166.72   12.152%   $186.9798   $186.98   $187.00   $187.00  
  Purchase #7 $64.42   3.504%   $66.6773   $66.68   $66.70   $66.70  
  7 purchase totals = $1,121.15       $1,214.7478   $1,214.75   $1,214.80   $1,214.70