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 $249.49   5.113%   $262.2464   $262.25   $262.25   $262.20  
  Purchase #2 $107.39   9.206%   $117.2763   $117.28   $117.30   $117.30  
  Purchase #3 $78.95   6.550%   $84.1212   $84.12   $84.10   $84.10  
  Purchase #4 $101.51   9.468%   $111.121   $111.12   $111.10   $111.10  
  Purchase #5 $185.27   10.709%   $205.1106   $205.11   $205.10   $205.10  
  Purchase #6 $5.63   13.816%   $6.4078   $6.41   $6.40   $6.40  
  Purchase #7 $109.63   10.151%   $120.7585   $120.76   $120.75   $120.80  
  7 purchase totals = $837.87       $907.0418   $907.05   $907.00   $907.00