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 $221.65   8.862%   $241.2926   $241.29   $241.30   $241.30  
  Purchase #2 $57.78   12.136%   $64.7922   $64.79   $64.80   $64.80  
  Purchase #3 $165.99   11.397%   $184.9079   $184.91   $184.90   $184.90  
  Purchase #4 $217.26   4.258%   $226.5109   $226.51   $226.50   $226.50  
  Purchase #5 $27.42   6.290%   $29.1447   $29.14   $29.15   $29.10  
  Purchase #6 $249.55   5.213%   $262.559   $262.56   $262.55   $262.60  
  Purchase #7 $206.40   13.133%   $233.5065   $233.51   $233.50   $233.50  
  7 purchase totals = $1,146.05       $1,242.7138   $1,242.71   $1,242.70   $1,242.70