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 $22.68   5.672%   $23.9664   $23.97   $23.95   $24.00  
  Purchase #2 $79.92   8.544%   $86.7484   $86.75   $86.75   $86.70  
  Purchase #3 $127.65   10.473%   $141.0188   $141.02   $141.00   $141.00  
  Purchase #4 $160.35   7.609%   $172.551   $172.55   $172.55   $172.60  
  Purchase #5 $244.66   8.550%   $265.5784   $265.58   $265.60   $265.60  
  Purchase #6 $157.85   5.188%   $166.0393   $166.04   $166.05   $166.00  
  Purchase #7 $193.38   3.226%   $199.6184   $199.62   $199.60   $199.60  
  7 purchase totals = $986.49       $1,055.5207   $1,055.53   $1,055.50   $1,055.50