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 $60.73   5.665%   $64.1704   $64.17   $64.15   $64.20  
  Purchase #2 $94.96   4.113%   $98.8657   $98.87   $98.85   $98.90  
  Purchase #3 $121.51   13.778%   $138.2516   $138.25   $138.25   $138.30  
  Purchase #4 $87.38   5.467%   $92.1571   $92.16   $92.15   $92.20  
  Purchase #5 $42.25   5.247%   $44.4669   $44.47   $44.45   $44.50  
  Purchase #6 $68.90   7.745%   $74.2363   $74.24   $74.25   $74.20  
  Purchase #7 $247.99   4.501%   $259.152   $259.15   $259.15   $259.20  
  7 purchase totals = $723.72       $771.3000   $771.31   $771.25   $771.50