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 $48.83   11.368%   $54.381   $54.38   $54.40   $54.40  
  Purchase #2 $10.74   5.295%   $11.3087   $11.31   $11.30   $11.30  
  Purchase #3 $242.69   9.201%   $265.0199   $265.02   $265.00   $265.00  
  Purchase #4 $11.45   8.576%   $12.432   $12.43   $12.45   $12.40  
  Purchase #5 $99.46   5.186%   $104.618   $104.62   $104.60   $104.60  
  Purchase #6 $83.99   3.768%   $87.1547   $87.15   $87.15   $87.20  
  Purchase #7 $245.40   9.809%   $269.4713   $269.47   $269.45   $269.50  
  7 purchase totals = $742.56       $804.3856   $804.38   $804.35   $804.40