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 $46.41   7.530%   $49.9047   $49.90   $49.90   $49.90  
  Purchase #2 $185.74   5.129%   $195.2666   $195.27   $195.25   $195.30  
  Purchase #3 $245.84   3.471%   $254.3731   $254.37   $254.35   $254.40  
  Purchase #4 $98.87   7.425%   $106.2111   $106.21   $106.20   $106.20  
  Purchase #5 $127.33   11.771%   $142.318   $142.32   $142.30   $142.30  
  Purchase #6 $229.82   3.749%   $238.436   $238.44   $238.45   $238.40  
  Purchase #7 $196.99   11.739%   $220.1147   $220.11   $220.10   $220.10  
  7 purchase totals = $1,131.00       $1,206.6242   $1,206.62   $1,206.55   $1,206.60