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 $242.86   4.197%   $253.0528   $253.05   $253.05   $253.10  
  Purchase #2 $220.78   11.288%   $245.7016   $245.70   $245.70   $245.70  
  Purchase #3 $68.46   9.174%   $74.7405   $74.74   $74.75   $74.70  
  Purchase #4 $170.85   13.285%   $193.5474   $193.55   $193.55   $193.50  
  Purchase #5 $32.61   5.788%   $34.4975   $34.50   $34.50   $34.50  
  Purchase #6 $49.56   8.132%   $53.5902   $53.59   $53.60   $53.60  
  Purchase #7 $97.55   7.624%   $104.9872   $104.99   $105.00   $105.00  
  7 purchase totals = $882.67       $960.1172   $960.12   $960.15   $960.10