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 $173.77   12.395%   $195.3088   $195.31   $195.30   $195.30  
  Purchase #2 $22.41   8.379%   $24.2877   $24.29   $24.30   $24.30  
  Purchase #3 $185.32   5.699%   $195.8814   $195.88   $195.90   $195.90  
  Purchase #4 $15.72   8.463%   $17.0504   $17.05   $17.05   $17.10  
  Purchase #5 $86.95   8.275%   $94.1451   $94.15   $94.15   $94.10  
  Purchase #6 $62.72   5.592%   $66.2273   $66.23   $66.25   $66.20  
  Purchase #7 $199.90   4.294%   $208.4837   $208.48   $208.50   $208.50  
  7 purchase totals = $746.79       $801.3844   $801.39   $801.45   $801.40