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 $64.72   13.212%   $73.2708   $73.27   $73.25   $73.30  
  Purchase #2 $112.29   4.593%   $117.4475   $117.45   $117.45   $117.40  
  Purchase #3 $147.38   13.616%   $167.4473   $167.45   $167.45   $167.40  
  Purchase #4 $248.78   7.258%   $266.8365   $266.84   $266.85   $266.80  
  Purchase #5 $30.53   7.198%   $32.7275   $32.73   $32.75   $32.70  
  Purchase #6 $77.49   6.271%   $82.3494   $82.35   $82.35   $82.30  
  Purchase #7 $107.43   3.208%   $110.8764   $110.88   $110.90   $110.90  
  7 purchase totals = $788.62       $850.9554   $850.97   $851.00   $850.80