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 $87.47   12.339%   $98.2629   $98.26   $98.25   $98.30  
  Purchase #2 $49.58   5.454%   $52.2841   $52.28   $52.30   $52.30  
  Purchase #3 $161.48   4.597%   $168.9032   $168.90   $168.90   $168.90  
  Purchase #4 $240.26   6.241%   $255.2546   $255.25   $255.25   $255.30  
  Purchase #5 $48.82   8.725%   $53.0795   $53.08   $53.10   $53.10  
  Purchase #6 $173.30   11.159%   $192.6385   $192.64   $192.65   $192.60  
  Purchase #7 $8.75   4.362%   $9.1317   $9.13   $9.15   $9.10  
  7 purchase totals = $769.66       $829.5545   $829.54   $829.60   $829.60