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 $241.27   10.177%   $265.824   $265.82   $265.80   $265.80  
  Purchase #2 $75.33   9.439%   $82.4404   $82.44   $82.45   $82.40  
  Purchase #3 $50.62   9.439%   $55.398   $55.40   $55.40   $55.40  
  Purchase #4 $130.87   7.675%   $140.9143   $140.91   $140.90   $140.90  
  Purchase #5 $241.86   3.197%   $249.5923   $249.59   $249.60   $249.60  
  Purchase #6 $42.28   4.852%   $44.3314   $44.33   $44.35   $44.30  
  Purchase #7 $196.94   8.500%   $213.6799   $213.68   $213.70   $213.70  
  7 purchase totals = $979.17       $1,052.1803   $1,052.17   $1,052.20   $1,052.10