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 $234.95   3.131%   $242.3063   $242.31   $242.30   $242.30  
  Purchase #2 $226.83   8.198%   $245.4255   $245.43   $245.45   $245.40  
  Purchase #3 $250.63   12.652%   $282.3397   $282.34   $282.35   $282.30  
  Purchase #4 $104.68   3.676%   $108.528   $108.53   $108.55   $108.50  
  Purchase #5 $50.48   4.485%   $52.744   $52.74   $52.75   $52.70  
  Purchase #6 $141.55   7.455%   $152.1026   $152.10   $152.10   $152.10  
  Purchase #7 $12.97   13.552%   $14.7277   $14.73   $14.75   $14.70  
  7 purchase totals = $1,022.09       $1,098.1738   $1,098.18   $1,098.25   $1,098.00