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 $86.65   10.246%   $95.5282   $95.53   $95.55   $95.50  
  Purchase #2 $47.51   5.181%   $49.9715   $49.97   $49.95   $50.00  
  Purchase #3 $151.31   11.749%   $169.0874   $169.09   $169.10   $169.10  
  Purchase #4 $75.38   13.547%   $85.5917   $85.59   $85.60   $85.60  
  Purchase #5 $74.94   11.523%   $83.5753   $83.58   $83.60   $83.60  
  Purchase #6 $182.47   8.155%   $197.3504   $197.35   $197.35   $197.40  
  Purchase #7 $86.51   8.662%   $94.0035   $94.00   $94.00   $94.00  
  7 purchase totals = $704.77       $775.1080   $775.11   $775.15   $775.20