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 $41.98   13.687%   $47.7258   $47.73   $47.75   $47.70  
  Purchase #2 $163.48   13.752%   $185.9618   $185.96   $185.95   $186.00  
  Purchase #3 $146.77   8.234%   $158.855   $158.86   $158.85   $158.90  
  Purchase #4 $179.90   7.405%   $193.2216   $193.22   $193.20   $193.20  
  Purchase #5 $81.83   10.545%   $90.459   $90.46   $90.45   $90.50  
  Purchase #6 $48.80   7.588%   $52.5029   $52.50   $52.50   $52.50  
  Purchase #7 $73.47   5.126%   $77.2361   $77.24   $77.25   $77.20  
  7 purchase totals = $736.23       $805.9622   $805.97   $805.95   $806.00