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 $193.73   5.797%   $204.9605   $204.96   $204.95   $205.00  
  Purchase #2 $225.64   3.598%   $233.7585   $233.76   $233.75   $233.80  
  Purchase #3 $113.63   11.236%   $126.3975   $126.40   $126.40   $126.40  
  Purchase #4 $24.28   12.802%   $27.3883   $27.39   $27.40   $27.40  
  Purchase #5 $138.97   13.671%   $157.9686   $157.97   $157.95   $158.00  
  Purchase #6 $24.42   5.275%   $25.7082   $25.71   $25.70   $25.70  
  Purchase #7 $163.88   5.649%   $173.1376   $173.14   $173.15   $173.10  
  7 purchase totals = $884.55       $949.3192   $949.33   $949.30   $949.40