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 $216.61   10.475%   $239.2999   $239.30   $239.30   $239.30  
  Purchase #2 $15.59   5.158%   $16.3941   $16.39   $16.40   $16.40  
  Purchase #3 $75.43   3.374%   $77.975   $77.98   $78.00   $78.00  
  Purchase #4 $15.45   4.660%   $16.17   $16.17   $16.15   $16.20  
  Purchase #5 $121.86   7.197%   $130.6303   $130.63   $130.65   $130.60  
  Purchase #6 $213.91   11.562%   $238.6423   $238.64   $238.65   $238.60  
  Purchase #7 $46.57   3.140%   $48.0323   $48.03   $48.05   $48.00  
  7 purchase totals = $705.42       $767.1439   $767.14   $767.20   $767.10