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 $56.63   6.817%   $60.4905   $60.49   $60.50   $60.50  
  Purchase #2 $84.63   4.292%   $88.2623   $88.26   $88.25   $88.30  
  Purchase #3 $8.28   10.152%   $9.1206   $9.12   $9.10   $9.10  
  Purchase #4 $72.66   7.736%   $78.281   $78.28   $78.30   $78.30  
  Purchase #5 $170.80   4.171%   $177.9241   $177.92   $177.90   $177.90  
  Purchase #6 $207.88   13.856%   $236.6839   $236.68   $236.70   $236.70  
  Purchase #7 $130.50   5.716%   $137.9594   $137.96   $137.95   $138.00  
  7 purchase totals = $731.38       $788.7218   $788.71   $788.70   $788.80