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 $62.54   4.247%   $65.1961   $65.20   $65.20   $65.20  
  Purchase #2 $229.59   13.660%   $260.952   $260.95   $260.95   $261.00  
  Purchase #3 $37.37   9.789%   $41.0281   $41.03   $41.05   $41.00  
  Purchase #4 $212.53   12.799%   $239.7317   $239.73   $239.75   $239.70  
  Purchase #5 $21.43   12.549%   $24.1193   $24.12   $24.10   $24.10  
  Purchase #6 $119.91   7.159%   $128.4944   $128.49   $128.50   $128.50  
  Purchase #7 $105.57   6.518%   $112.4511   $112.45   $112.45   $112.50  
  7 purchase totals = $788.94       $871.9727   $871.97   $872.00   $872.00