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 $239.38   10.280%   $263.9883   $263.99   $264.00   $264.00  
  Purchase #2 $156.90   5.415%   $165.3961   $165.40   $165.40   $165.40  
  Purchase #3 $161.49   10.560%   $178.5433   $178.54   $178.55   $178.50  
  Purchase #4 $82.80   4.134%   $86.223   $86.22   $86.20   $86.20  
  Purchase #5 $34.55   6.513%   $36.8002   $36.80   $36.80   $36.80  
  Purchase #6 $47.33   3.528%   $48.9998   $49.00   $49.00   $49.00  
  Purchase #7 $66.92   9.247%   $73.1081   $73.11   $73.10   $73.10  
  7 purchase totals = $789.37       $853.0588   $853.06   $853.05   $853.00