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 $70.62   7.154%   $75.6722   $75.67   $75.65   $75.70  
  Purchase #2 $32.92   11.727%   $36.7805   $36.78   $36.80   $36.80  
  Purchase #3 $68.83   11.742%   $76.912   $76.91   $76.90   $76.90  
  Purchase #4 $32.37   10.531%   $35.7789   $35.78   $35.80   $35.80  
  Purchase #5 $82.46   7.431%   $88.5876   $88.59   $88.60   $88.60  
  Purchase #6 $66.90   13.833%   $76.1543   $76.15   $76.15   $76.20  
  Purchase #7 $100.27   4.531%   $104.8132   $104.81   $104.80   $104.80  
  7 purchase totals = $454.37       $494.6987   $494.69   $494.70   $494.80