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 $226.98   11.549%   $253.1939   $253.19   $253.20   $253.20  
  Purchase #2 $46.34   11.627%   $51.728   $51.73   $51.75   $51.70  
  Purchase #3 $7.54   8.872%   $8.2089   $8.21   $8.20   $8.20  
  Purchase #4 $146.83   4.714%   $153.7516   $153.75   $153.75   $153.80  
  Purchase #5 $247.86   3.154%   $255.6775   $255.68   $255.70   $255.70  
  Purchase #6 $176.81   3.463%   $182.9329   $182.93   $182.95   $182.90  
  Purchase #7 $42.41   11.381%   $47.2367   $47.24   $47.25   $47.20  
  7 purchase totals = $894.77       $952.7295   $952.73   $952.80   $952.70