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 $211.71   4.402%   $221.0295   $221.03   $221.05   $221.00  
  Purchase #2 $57.98   11.292%   $64.5271   $64.53   $64.55   $64.50  
  Purchase #3 $183.78   7.139%   $196.9001   $196.90   $196.90   $196.90  
  Purchase #4 $151.64   9.707%   $166.3597   $166.36   $166.35   $166.40  
  Purchase #5 $240.54   5.209%   $253.0697   $253.07   $253.05   $253.10  
  Purchase #6 $50.63   13.806%   $57.62   $57.62   $57.60   $57.60  
  Purchase #7 $108.97   8.450%   $118.178   $118.18   $118.20   $118.20  
  7 purchase totals = $1,005.25       $1,077.6841   $1,077.69   $1,077.70   $1,077.70