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 $62.76   3.591%   $65.0137   $65.01   $65.00   $65.00  
  Purchase #2 $239.58   6.827%   $255.9361   $255.94   $255.95   $255.90  
  Purchase #3 $178.78   5.207%   $188.0891   $188.09   $188.10   $188.10  
  Purchase #4 $222.61   8.110%   $240.6637   $240.66   $240.65   $240.70  
  Purchase #5 $229.62   11.398%   $255.7921   $255.79   $255.80   $255.80  
  Purchase #6 $126.62   4.693%   $132.5623   $132.56   $132.55   $132.60  
  Purchase #7 $133.76   4.833%   $140.2246   $140.22   $140.20   $140.20  
  7 purchase totals = $1,193.73       $1,278.2816   $1,278.27   $1,278.25   $1,278.30