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 $59.66   13.317%   $67.6049   $67.60   $67.60   $67.60  
  Purchase #2 $125.81   3.759%   $130.5392   $130.54   $130.55   $130.50  
  Purchase #3 $192.42   10.706%   $213.0205   $213.02   $213.00   $213.00  
  Purchase #4 $219.77   5.680%   $232.2529   $232.25   $232.25   $232.30  
  Purchase #5 $248.39   11.163%   $276.1178   $276.12   $276.10   $276.10  
  Purchase #6 $228.62   11.534%   $254.989   $254.99   $255.00   $255.00  
  Purchase #7 $157.39   11.382%   $175.3041   $175.30   $175.30   $175.30  
  7 purchase totals = $1,232.06       $1,349.8284   $1,349.82   $1,349.80   $1,349.80