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 $244.95   8.675%   $266.1994   $266.20   $266.20   $266.20  
  Purchase #2 $21.92   6.113%   $23.26   $23.26   $23.25   $23.30  
  Purchase #3 $103.78   13.136%   $117.4125   $117.41   $117.40   $117.40  
  Purchase #4 $211.29   13.226%   $239.2352   $239.24   $239.25   $239.20  
  Purchase #5 $103.54   7.733%   $111.5467   $111.55   $111.55   $111.50  
  Purchase #6 $236.94   4.277%   $247.0739   $247.07   $247.05   $247.10  
  Purchase #7 $30.36   4.169%   $31.6257   $31.63   $31.65   $31.60  
  7 purchase totals = $952.78       $1,036.3534   $1,036.36   $1,036.35   $1,036.30