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 $123.95   8.855%   $134.9258   $134.93   $134.95   $134.90  
  Purchase #2 $49.32   10.387%   $54.4429   $54.44   $54.45   $54.40  
  Purchase #3 $58.36   8.135%   $63.1076   $63.11   $63.10   $63.10  
  Purchase #4 $13.86   11.643%   $15.4737   $15.47   $15.45   $15.50  
  Purchase #5 $195.88   13.581%   $222.4825   $222.48   $222.50   $222.50  
  Purchase #6 $221.33   5.488%   $233.4766   $233.48   $233.50   $233.50  
  Purchase #7 $205.43   12.628%   $231.3717   $231.37   $231.35   $231.40  
  7 purchase totals = $868.13       $955.2808   $955.28   $955.30   $955.30