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 $58.44   8.728%   $63.5406   $63.54   $63.55   $63.50  
  Purchase #2 $164.29   3.735%   $170.4262   $170.43   $170.45   $170.40  
  Purchase #3 $42.26   10.110%   $46.5325   $46.53   $46.55   $46.50  
  Purchase #4 $132.63   12.145%   $148.7379   $148.74   $148.75   $148.70  
  Purchase #5 $208.42   8.568%   $226.2774   $226.28   $226.30   $226.30  
  Purchase #6 $228.70   9.744%   $250.9845   $250.98   $251.00   $251.00  
  Purchase #7 $26.56   7.300%   $28.4989   $28.50   $28.50   $28.50  
  7 purchase totals = $861.30       $934.9980   $935.00   $935.10   $934.90