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 $65.25   12.276%   $73.2601   $73.26   $73.25   $73.30  
  Purchase #2 $18.48   3.644%   $19.1534   $19.15   $19.15   $19.20  
  Purchase #3 $96.45   6.296%   $102.5225   $102.52   $102.50   $102.50  
  Purchase #4 $179.93   5.726%   $190.2328   $190.23   $190.25   $190.20  
  Purchase #5 $198.60   6.540%   $211.5884   $211.59   $211.60   $211.60  
  Purchase #6 $250.34   4.424%   $261.415   $261.42   $261.40   $261.40  
  Purchase #7 $75.42   11.656%   $84.211   $84.21   $84.20   $84.20  
  7 purchase totals = $884.47       $942.3832   $942.38   $942.35   $942.40