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 $239.63   5.591%   $253.0277   $253.03   $253.05   $253.00  
  Purchase #2 $166.91   12.167%   $187.2179   $187.22   $187.20   $187.20  
  Purchase #3 $188.26   10.680%   $208.3662   $208.37   $208.35   $208.40  
  Purchase #4 $181.71   13.639%   $206.4934   $206.49   $206.50   $206.50  
  Purchase #5 $221.90   5.403%   $233.8893   $233.89   $233.90   $233.90  
  Purchase #6 $31.34   4.708%   $32.8155   $32.82   $32.80   $32.80  
  Purchase #7 $169.69   3.832%   $176.1925   $176.19   $176.20   $176.20  
  7 purchase totals = $1,199.44       $1,298.0025   $1,298.01   $1,298.00   $1,298.00