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 $6.44   5.723%   $6.8086   $6.81   $6.80   $6.80  
  Purchase #2 $148.30   7.482%   $159.3958   $159.40   $159.40   $159.40  
  Purchase #3 $35.38   4.263%   $36.8882   $36.89   $36.90   $36.90  
  Purchase #4 $30.63   7.187%   $32.8314   $32.83   $32.85   $32.80  
  Purchase #5 $33.34   11.856%   $37.2928   $37.29   $37.30   $37.30  
  Purchase #6 $239.64   10.787%   $265.49   $265.49   $265.50   $265.50  
  Purchase #7 $186.68   6.656%   $199.1054   $199.11   $199.10   $199.10  
  7 purchase totals = $680.41       $737.8122   $737.82   $737.85   $737.80