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 $56.28   8.209%   $60.9   $60.90   $60.90   $60.90  
  Purchase #2 $88.32   9.384%   $96.6079   $96.61   $96.60   $96.60  
  Purchase #3 $161.90   3.337%   $167.3026   $167.30   $167.30   $167.30  
  Purchase #4 $164.78   11.288%   $183.3804   $183.38   $183.40   $183.40  
  Purchase #5 $109.61   5.438%   $115.5706   $115.57   $115.55   $115.60  
  Purchase #6 $108.49   10.249%   $119.6091   $119.61   $119.60   $119.60  
  Purchase #7 $42.31   5.463%   $44.6214   $44.62   $44.60   $44.60  
  7 purchase totals = $731.69       $787.9920   $787.99   $787.95   $788.00