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 $14.63   3.558%   $15.1505   $15.15   $15.15   $15.20  
  Purchase #2 $233.93   8.558%   $253.9497   $253.95   $253.95   $253.90  
  Purchase #3 $98.63   8.551%   $107.0639   $107.06   $107.05   $107.10  
  Purchase #4 $169.48   11.145%   $188.3685   $188.37   $188.35   $188.40  
  Purchase #5 $250.33   11.828%   $279.939   $279.94   $279.95   $279.90  
  Purchase #6 $121.56   10.450%   $134.263   $134.26   $134.25   $134.30  
  Purchase #7 $124.77   10.291%   $137.6101   $137.61   $137.60   $137.60  
  7 purchase totals = $1,013.33       $1,116.3447   $1,116.34   $1,116.30   $1,116.40