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 $188.75   9.812%   $207.2702   $207.27   $207.25   $207.30  
  Purchase #2 $74.93   12.335%   $84.1726   $84.17   $84.15   $84.20  
  Purchase #3 $149.96   7.105%   $160.6147   $160.61   $160.60   $160.60  
  Purchase #4 $11.41   4.764%   $11.9536   $11.95   $11.95   $12.00  
  Purchase #5 $67.74   8.216%   $73.3055   $73.31   $73.30   $73.30  
  Purchase #6 $92.62   4.105%   $96.4221   $96.42   $96.40   $96.40  
  Purchase #7 $230.55   13.620%   $261.9509   $261.95   $261.95   $262.00  
  7 purchase totals = $815.96       $895.6896   $895.68   $895.60   $895.80