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 $214.51   8.497%   $232.7369   $232.74   $232.75   $232.70  
  Purchase #2 $42.90   12.126%   $48.1021   $48.10   $48.10   $48.10  
  Purchase #3 $154.30   6.683%   $164.6119   $164.61   $164.60   $164.60  
  Purchase #4 $42.37   10.779%   $46.9371   $46.94   $46.95   $46.90  
  Purchase #5 $66.83   8.252%   $72.3448   $72.34   $72.35   $72.30  
  Purchase #6 $186.61   5.842%   $197.5118   $197.51   $197.50   $197.50  
  Purchase #7 $154.55   10.633%   $170.9833   $170.98   $171.00   $171.00  
  7 purchase totals = $862.07       $933.2279   $933.22   $933.25   $933.10