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 $58.57   7.628%   $63.0377   $63.04   $63.05   $63.00  
  Purchase #2 $231.38   5.589%   $244.3118   $244.31   $244.30   $244.30  
  Purchase #3 $47.26   13.567%   $53.6718   $53.67   $53.65   $53.70  
  Purchase #4 $40.82   12.775%   $46.0348   $46.03   $46.05   $46.00  
  Purchase #5 $92.25   5.284%   $97.1245   $97.12   $97.10   $97.10  
  Purchase #6 $210.81   5.681%   $222.7861   $222.79   $222.80   $222.80  
  Purchase #7 $239.27   13.567%   $271.7318   $271.73   $271.75   $271.70  
  7 purchase totals = $920.36       $998.6985   $998.69   $998.70   $998.60