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 $58.34   13.613%   $66.2818   $66.28   $66.30   $66.30  
  Purchase #2 $195.25   8.298%   $211.4518   $211.45   $211.45   $211.50  
  Purchase #3 $207.93   13.734%   $236.4871   $236.49   $236.50   $236.50  
  Purchase #4 $15.75   8.221%   $17.0448   $17.04   $17.05   $17.00  
  Purchase #5 $101.27   11.355%   $112.7692   $112.77   $112.75   $112.80  
  Purchase #6 $227.88   3.778%   $236.4893   $236.49   $236.50   $236.50  
  Purchase #7 $42.48   4.295%   $44.3045   $44.30   $44.30   $44.30  
  7 purchase totals = $848.90       $924.8285   $924.82   $924.85   $924.90