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 $215.53   13.266%   $244.1222   $244.12   $244.10   $244.10  
  Purchase #2 $40.42   10.321%   $44.5917   $44.59   $44.60   $44.60  
  Purchase #3 $44.26   11.202%   $49.218   $49.22   $49.20   $49.20  
  Purchase #4 $35.97   8.252%   $38.9382   $38.94   $38.95   $38.90  
  Purchase #5 $80.36   12.664%   $90.5368   $90.54   $90.55   $90.50  
  Purchase #6 $207.30   12.610%   $233.4405   $233.44   $233.45   $233.40  
  Purchase #7 $176.38   12.172%   $197.849   $197.85   $197.85   $197.80  
  7 purchase totals = $800.22       $898.6964   $898.70   $898.70   $898.50