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 $168.73   4.430%   $176.2047   $176.20   $176.20   $176.20  
  Purchase #2 $245.49   8.620%   $266.6512   $266.65   $266.65   $266.70  
  Purchase #3 $53.40   3.220%   $55.1195   $55.12   $55.10   $55.10  
  Purchase #4 $176.76   3.615%   $183.1499   $183.15   $183.15   $183.10  
  Purchase #5 $60.60   6.303%   $64.4196   $64.42   $64.40   $64.40  
  Purchase #6 $36.93   8.220%   $39.9656   $39.97   $39.95   $40.00  
  Purchase #7 $76.34   13.464%   $86.6184   $86.62   $86.60   $86.60  
  7 purchase totals = $818.25       $872.1289   $872.13   $872.05   $872.10