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 $33.29   9.692%   $36.5165   $36.52   $36.50   $36.50  
  Purchase #2 $193.28   11.615%   $215.7295   $215.73   $215.75   $215.70  
  Purchase #3 $25.39   8.279%   $27.492   $27.49   $27.50   $27.50  
  Purchase #4 $81.44   6.756%   $86.9421   $86.94   $86.95   $86.90  
  Purchase #5 $127.26   4.663%   $133.1941   $133.19   $133.20   $133.20  
  Purchase #6 $231.38   8.225%   $250.411   $250.41   $250.40   $250.40  
  Purchase #7 $190.91   5.422%   $201.2611   $201.26   $201.25   $201.30  
  7 purchase totals = $882.95       $951.5463   $951.54   $951.55   $951.50