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 $114.79   12.613%   $129.2685   $129.27   $129.25   $129.30  
  Purchase #2 $217.25   7.665%   $233.9022   $233.90   $233.90   $233.90  
  Purchase #3 $140.34   8.302%   $151.991   $151.99   $152.00   $152.00  
  Purchase #4 $191.37   11.660%   $213.6837   $213.68   $213.70   $213.70  
  Purchase #5 $230.43   9.103%   $251.406   $251.41   $251.40   $251.40  
  Purchase #6 $241.29   8.874%   $262.7021   $262.70   $262.70   $262.70  
  Purchase #7 $27.35   8.433%   $29.6564   $29.66   $29.65   $29.70  
  7 purchase totals = $1,162.82       $1,272.6099   $1,272.61   $1,272.60   $1,272.70