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 $194.54   12.749%   $219.3419   $219.34   $219.35   $219.30  
  Purchase #2 $207.92   3.183%   $214.5381   $214.54   $214.55   $214.50  
  Purchase #3 $15.47   8.453%   $16.7777   $16.78   $16.80   $16.80  
  Purchase #4 $51.49   4.697%   $53.9085   $53.91   $53.90   $53.90  
  Purchase #5 $31.82   13.432%   $36.0941   $36.09   $36.10   $36.10  
  Purchase #6 $136.49   3.643%   $141.4623   $141.46   $141.45   $141.50  
  Purchase #7 $246.75   6.123%   $261.8585   $261.86   $261.85   $261.90  
  7 purchase totals = $884.48       $943.9811   $943.98   $944.00   $944.00