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 $22.84   12.179%   $25.6217   $25.62   $25.60   $25.60  
  Purchase #2 $182.90   8.355%   $198.1813   $198.18   $198.20   $198.20  
  Purchase #3 $224.62   7.438%   $241.3272   $241.33   $241.35   $241.30  
  Purchase #4 $45.69   12.562%   $51.4296   $51.43   $51.45   $51.40  
  Purchase #5 $61.92   7.591%   $66.6203   $66.62   $66.60   $66.60  
  Purchase #6 $245.50   9.357%   $268.4714   $268.47   $268.45   $268.50  
  Purchase #7 $97.63   6.748%   $104.2181   $104.22   $104.20   $104.20  
  7 purchase totals = $881.10       $955.8696   $955.87   $955.85   $955.80