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 $190.96   5.527%   $201.5144   $201.51   $201.50   $201.50  
  Purchase #2 $193.50   12.376%   $217.4476   $217.45   $217.45   $217.40  
  Purchase #3 $249.41   12.484%   $280.5463   $280.55   $280.55   $280.50  
  Purchase #4 $44.59   8.164%   $48.2303   $48.23   $48.25   $48.20  
  Purchase #5 $98.86   8.428%   $107.1919   $107.19   $107.20   $107.20  
  Purchase #6 $195.77   9.775%   $214.9065   $214.91   $214.90   $214.90  
  Purchase #7 $226.28   4.440%   $236.3268   $236.33   $236.35   $236.30  
  7 purchase totals = $1,199.37       $1,306.1638   $1,306.17   $1,306.20   $1,306.00