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 $161.69   12.588%   $182.0435   $182.04   $182.05   $182.00  
  Purchase #2 $188.45   10.755%   $208.7178   $208.72   $208.70   $208.70  
  Purchase #3 $61.48   4.516%   $64.2564   $64.26   $64.25   $64.30  
  Purchase #4 $233.95   3.620%   $242.419   $242.42   $242.40   $242.40  
  Purchase #5 $250.85   8.253%   $271.5527   $271.55   $271.55   $271.60  
  Purchase #6 $83.79   7.318%   $89.9218   $89.92   $89.90   $89.90  
  Purchase #7 $133.74   8.332%   $144.8832   $144.88   $144.90   $144.90  
  7 purchase totals = $1,113.95       $1,203.7944   $1,203.79   $1,203.75   $1,203.80