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 $60.63   8.450%   $65.7532   $65.75   $65.75   $65.80  
  Purchase #2 $112.49   6.516%   $119.8198   $119.82   $119.80   $119.80  
  Purchase #3 $221.68   5.183%   $233.1697   $233.17   $233.15   $233.20  
  Purchase #4 $48.48   6.431%   $51.5977   $51.60   $51.60   $51.60  
  Purchase #5 $95.98   6.425%   $102.1467   $102.15   $102.15   $102.10  
  Purchase #6 $159.82   4.152%   $166.4557   $166.46   $166.45   $166.50  
  Purchase #7 $153.91   13.455%   $174.6186   $174.62   $174.60   $174.60  
  7 purchase totals = $852.99       $913.5614   $913.57   $913.50   $913.60