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 $61.43   13.226%   $69.5547   $69.55   $69.55   $69.60  
  Purchase #2 $25.61   11.780%   $28.6269   $28.63   $28.65   $28.60  
  Purchase #3 $70.60   7.591%   $75.9592   $75.96   $75.95   $76.00  
  Purchase #4 $158.69   11.761%   $177.3535   $177.35   $177.35   $177.40  
  Purchase #5 $95.98   6.456%   $102.1765   $102.18   $102.20   $102.20  
  Purchase #6 $92.83   9.338%   $101.4985   $101.50   $101.50   $101.50  
  Purchase #7 $49.80   3.710%   $51.6476   $51.65   $51.65   $51.60  
  7 purchase totals = $554.94       $606.8169   $606.82   $606.85   $606.90