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 $84.37   9.741%   $92.5885   $92.59   $92.60   $92.60  
  Purchase #2 $185.56   5.483%   $195.7343   $195.73   $195.75   $195.70  
  Purchase #3 $242.86   7.457%   $260.9701   $260.97   $260.95   $261.00  
  Purchase #4 $47.85   13.838%   $54.4715   $54.47   $54.45   $54.50  
  Purchase #5 $174.44   4.750%   $182.7259   $182.73   $182.75   $182.70  
  Purchase #6 $32.51   8.606%   $35.3078   $35.31   $35.30   $35.30  
  Purchase #7 $60.44   12.210%   $67.8197   $67.82   $67.80   $67.80  
  7 purchase totals = $828.03       $889.6178   $889.62   $889.60   $889.60