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 $236.63   10.136%   $260.6148   $260.61   $260.60   $260.60  
  Purchase #2 $213.98   11.195%   $237.9351   $237.94   $237.95   $237.90  
  Purchase #3 $7.32   11.121%   $8.1341   $8.13   $8.15   $8.10  
  Purchase #4 $107.62   7.801%   $116.0154   $116.02   $116.00   $116.00  
  Purchase #5 $174.89   10.763%   $193.7134   $193.71   $193.70   $193.70  
  Purchase #6 $186.27   8.163%   $201.4752   $201.48   $201.50   $201.50  
  Purchase #7 $198.26   8.849%   $215.804   $215.80   $215.80   $215.80  
  7 purchase totals = $1,124.97       $1,233.6920   $1,233.69   $1,233.70   $1,233.60