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 $66.35   10.210%   $73.1243   $73.12   $73.10   $73.10  
  Purchase #2 $207.50   11.756%   $231.8937   $231.89   $231.90   $231.90  
  Purchase #3 $87.96   8.868%   $95.7603   $95.76   $95.75   $95.80  
  Purchase #4 $204.98   9.463%   $224.3773   $224.38   $224.40   $224.40  
  Purchase #5 $83.51   8.303%   $90.4438   $90.44   $90.45   $90.40  
  Purchase #6 $45.86   13.585%   $52.0901   $52.09   $52.10   $52.10  
  Purchase #7 $59.28   8.528%   $64.3354   $64.34   $64.35   $64.30  
  7 purchase totals = $755.44       $832.0249   $832.02   $832.05   $832.00