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 $18.71   9.847%   $20.5524   $20.55   $20.55   $20.60  
  Purchase #2 $207.40   9.496%   $227.0947   $227.09   $227.10   $227.10  
  Purchase #3 $105.87   5.765%   $111.9734   $111.97   $111.95   $112.00  
  Purchase #4 $33.34   7.371%   $35.7975   $35.80   $35.80   $35.80  
  Purchase #5 $8.74   13.537%   $9.9231   $9.92   $9.90   $9.90  
  Purchase #6 $243.73   3.352%   $251.8998   $251.90   $251.90   $251.90  
  Purchase #7 $38.46   11.145%   $42.7464   $42.75   $42.75   $42.70  
  7 purchase totals = $656.25       $699.9873   $699.98   $699.95   $700.00