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 $239.45   4.344%   $249.8517   $249.85   $249.85   $249.90  
  Purchase #2 $47.32   7.535%   $50.8856   $50.89   $50.90   $50.90  
  Purchase #3 $229.26   11.833%   $256.3883   $256.39   $256.40   $256.40  
  Purchase #4 $29.47   3.165%   $30.4027   $30.40   $30.40   $30.40  
  Purchase #5 $112.96   9.856%   $124.0933   $124.09   $124.10   $124.10  
  Purchase #6 $169.53   13.240%   $191.9758   $191.98   $192.00   $192.00  
  Purchase #7 $116.60   3.846%   $121.0844   $121.08   $121.10   $121.10  
  7 purchase totals = $944.59       $1,024.6818   $1,024.68   $1,024.75   $1,024.80