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 $216.79   10.532%   $239.6223   $239.62   $239.60   $239.60  
  Purchase #2 $169.78   13.501%   $192.702   $192.70   $192.70   $192.70  
  Purchase #3 $86.97   4.198%   $90.621   $90.62   $90.60   $90.60  
  Purchase #4 $61.49   7.464%   $66.0796   $66.08   $66.10   $66.10  
  Purchase #5 $81.47   13.345%   $92.3422   $92.34   $92.35   $92.30  
  Purchase #6 $69.86   6.141%   $74.1501   $74.15   $74.15   $74.20  
  Purchase #7 $161.41   4.649%   $168.914   $168.91   $168.90   $168.90  
  7 purchase totals = $847.77       $924.4312   $924.42   $924.40   $924.40