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 $111.41   12.716%   $125.5769   $125.58   $125.60   $125.60  
  Purchase #2 $237.66   12.309%   $266.9136   $266.91   $266.90   $266.90  
  Purchase #3 $119.47   10.130%   $131.5723   $131.57   $131.55   $131.60  
  Purchase #4 $199.64   9.444%   $218.494   $218.49   $218.50   $218.50  
  Purchase #5 $98.47   6.703%   $105.0704   $105.07   $105.05   $105.10  
  Purchase #6 $80.35   7.254%   $86.1786   $86.18   $86.20   $86.20  
  Purchase #7 $91.76   7.557%   $98.6943   $98.69   $98.70   $98.70  
  7 purchase totals = $938.76       $1,032.5001   $1,032.49   $1,032.50   $1,032.60