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 $81.36   8.334%   $88.1405   $88.14   $88.15   $88.10  
  Purchase #2 $224.97   8.263%   $243.5593   $243.56   $243.55   $243.60  
  Purchase #3 $119.59   3.805%   $124.1404   $124.14   $124.15   $124.10  
  Purchase #4 $84.44   10.848%   $93.6001   $93.60   $93.60   $93.60  
  Purchase #5 $209.42   10.129%   $230.6322   $230.63   $230.65   $230.60  
  Purchase #6 $26.38   5.222%   $27.7576   $27.76   $27.75   $27.80  
  Purchase #7 $120.66   4.791%   $126.4408   $126.44   $126.45   $126.40  
  7 purchase totals = $866.82       $934.2709   $934.27   $934.30   $934.20