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 $116.41   6.688%   $124.1955   $124.20   $124.20   $124.20  
  Purchase #2 $154.93   7.162%   $166.0261   $166.03   $166.05   $166.00  
  Purchase #3 $103.66   5.531%   $109.3934   $109.39   $109.40   $109.40  
  Purchase #4 $216.64   5.207%   $227.9204   $227.92   $227.90   $227.90  
  Purchase #5 $85.89   10.336%   $94.7676   $94.77   $94.75   $94.80  
  Purchase #6 $242.39   4.644%   $253.6466   $253.65   $253.65   $253.60  
  Purchase #7 $9.29   7.497%   $9.9865   $9.99   $10.00   $10.00  
  7 purchase totals = $929.21       $985.9361   $985.95   $985.95   $985.90