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 $88.74   10.614%   $98.1589   $98.16   $98.15   $98.20  
  Purchase #2 $59.75   4.788%   $62.6108   $62.61   $62.60   $62.60  
  Purchase #3 $115.99   13.203%   $131.3042   $131.30   $131.30   $131.30  
  Purchase #4 $97.29   13.241%   $110.1722   $110.17   $110.15   $110.20  
  Purchase #5 $139.77   8.331%   $151.4142   $151.41   $151.40   $151.40  
  Purchase #6 $10.38   10.111%   $11.4295   $11.43   $11.45   $11.40  
  Purchase #7 $226.58   5.796%   $239.7126   $239.71   $239.70   $239.70  
  7 purchase totals = $738.50       $804.8024   $804.79   $804.75   $804.80