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 $118.74   6.827%   $126.8464   $126.85   $126.85   $126.80  
  Purchase #2 $112.33   3.219%   $115.9459   $115.95   $115.95   $115.90  
  Purchase #3 $5.51   10.510%   $6.0891   $6.09   $6.10   $6.10  
  Purchase #4 $56.38   3.643%   $58.4339   $58.43   $58.45   $58.40  
  Purchase #5 $249.48   5.694%   $263.6854   $263.69   $263.70   $263.70  
  Purchase #6 $84.89   13.588%   $96.4249   $96.42   $96.40   $96.40  
  Purchase #7 $188.68   6.794%   $201.4989   $201.50   $201.50   $201.50  
  7 purchase totals = $816.01       $868.9245   $868.93   $868.95   $868.80