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 $216.45   4.510%   $226.2119   $226.21   $226.20   $226.20  
  Purchase #2 $217.87   8.479%   $236.3432   $236.34   $236.35   $236.30  
  Purchase #3 $107.79   6.592%   $114.8955   $114.90   $114.90   $114.90  
  Purchase #4 $245.92   11.431%   $274.0311   $274.03   $274.05   $274.00  
  Purchase #5 $68.91   9.574%   $75.5074   $75.51   $75.50   $75.50  
  Purchase #6 $91.98   9.848%   $101.0382   $101.04   $101.05   $101.00  
  Purchase #7 $206.73   11.864%   $231.2564   $231.26   $231.25   $231.30  
  7 purchase totals = $1,155.65       $1,259.2837   $1,259.29   $1,259.30   $1,259.20