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 $214.92   13.227%   $243.3475   $243.35   $243.35   $243.30  
  Purchase #2 $99.92   7.159%   $107.0733   $107.07   $107.05   $107.10  
  Purchase #3 $66.50   6.687%   $70.9469   $70.95   $70.95   $70.90  
  Purchase #4 $206.49   9.390%   $225.8794   $225.88   $225.90   $225.90  
  Purchase #5 $139.97   12.874%   $157.9897   $157.99   $158.00   $158.00  
  Purchase #6 $34.69   5.536%   $36.6104   $36.61   $36.60   $36.60  
  Purchase #7 $176.71   4.356%   $184.4075   $184.41   $184.40   $184.40  
  7 purchase totals = $939.20       $1,026.2547   $1,026.26   $1,026.25   $1,026.20