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 $175.53   13.510%   $199.2441   $199.24   $199.25   $199.20  
  Purchase #2 $23.84   11.817%   $26.6572   $26.66   $26.65   $26.70  
  Purchase #3 $46.71   5.494%   $49.2762   $49.28   $49.30   $49.30  
  Purchase #4 $86.87   4.284%   $90.5915   $90.59   $90.60   $90.60  
  Purchase #5 $233.64   3.810%   $242.5417   $242.54   $242.55   $242.50  
  Purchase #6 $183.83   13.243%   $208.1746   $208.17   $208.15   $208.20  
  Purchase #7 $217.78   11.131%   $242.0211   $242.02   $242.00   $242.00  
  7 purchase totals = $968.20       $1,058.5064   $1,058.50   $1,058.50   $1,058.50