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 $224.42   10.214%   $247.3423   $247.34   $247.35   $247.30  
  Purchase #2 $13.30   6.797%   $14.204   $14.20   $14.20   $14.20  
  Purchase #3 $201.63   7.127%   $216.0002   $216.00   $216.00   $216.00  
  Purchase #4 $40.40   7.616%   $43.4769   $43.48   $43.50   $43.50  
  Purchase #5 $46.31   11.199%   $51.4963   $51.50   $51.50   $51.50  
  Purchase #6 $33.56   3.495%   $34.7329   $34.73   $34.75   $34.70  
  Purchase #7 $241.53   7.305%   $259.1738   $259.17   $259.15   $259.20  
  7 purchase totals = $801.15       $866.4264   $866.42   $866.45   $866.40