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 $224.42   10.622%   $248.2579   $248.26   $248.25   $248.30  
  Purchase #2 $176.47   8.513%   $191.4929   $191.49   $191.50   $191.50  
  Purchase #3 $54.59   5.595%   $57.6443   $57.64   $57.65   $57.60  
  Purchase #4 $52.42   9.351%   $57.3218   $57.32   $57.30   $57.30  
  Purchase #5 $157.65   3.198%   $162.6916   $162.69   $162.70   $162.70  
  Purchase #6 $191.97   11.231%   $213.5302   $213.53   $213.55   $213.50  
  Purchase #7 $227.44   6.578%   $242.401   $242.40   $242.40   $242.40  
  7 purchase totals = $1,084.96       $1,173.3397   $1,173.33   $1,173.35   $1,173.30