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 $92.61   6.852%   $98.9556   $98.96   $98.95   $99.00  
  Purchase #2 $91.60   13.723%   $104.1703   $104.17   $104.15   $104.20  
  Purchase #3 $114.41   8.584%   $124.231   $124.23   $124.25   $124.20  
  Purchase #4 $93.35   6.103%   $99.0472   $99.05   $99.05   $99.00  
  Purchase #5 $76.63   7.519%   $82.3918   $82.39   $82.40   $82.40  
  Purchase #6 $25.28   3.375%   $26.1332   $26.13   $26.15   $26.10  
  Purchase #7 $217.32   3.242%   $224.3655   $224.37   $224.35   $224.40  
  7 purchase totals = $711.20       $759.2946   $759.30   $759.30   $759.30