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 $217.72   9.410%   $238.2075   $238.21   $238.20   $238.20  
  Purchase #2 $188.37   11.159%   $209.3902   $209.39   $209.40   $209.40  
  Purchase #3 $156.90   12.515%   $176.536   $176.54   $176.55   $176.50  
  Purchase #4 $223.74   8.538%   $242.8429   $242.84   $242.85   $242.80  
  Purchase #5 $222.63   13.269%   $252.1708   $252.17   $252.15   $252.20  
  Purchase #6 $185.27   13.105%   $209.5496   $209.55   $209.55   $209.50  
  Purchase #7 $118.47   5.688%   $125.2086   $125.21   $125.20   $125.20  
  7 purchase totals = $1,313.10       $1,453.9056   $1,453.91   $1,453.90   $1,453.80