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 $188.31   10.470%   $208.0261   $208.03   $208.05   $208.00  
  Purchase #2 $176.29   4.217%   $183.7241   $183.72   $183.70   $183.70  
  Purchase #3 $48.36   9.205%   $52.8115   $52.81   $52.80   $52.80  
  Purchase #4 $184.73   11.660%   $206.2695   $206.27   $206.25   $206.30  
  Purchase #5 $27.44   10.438%   $30.3042   $30.30   $30.30   $30.30  
  Purchase #6 $46.77   9.863%   $51.3829   $51.38   $51.40   $51.40  
  Purchase #7 $73.40   7.339%   $78.7868   $78.79   $78.80   $78.80  
  7 purchase totals = $745.30       $811.3051   $811.30   $811.30   $811.30