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 $236.93   12.364%   $266.224   $266.22   $266.20   $266.20  
  Purchase #2 $9.63   10.532%   $10.6442   $10.64   $10.65   $10.60  
  Purchase #3 $13.38   8.150%   $14.4705   $14.47   $14.45   $14.50  
  Purchase #4 $121.53   9.172%   $132.6767   $132.68   $132.70   $132.70  
  Purchase #5 $100.81   13.682%   $114.6028   $114.60   $114.60   $114.60  
  Purchase #6 $159.38   3.303%   $164.6443   $164.64   $164.65   $164.60  
  Purchase #7 $60.94   13.378%   $69.0926   $69.09   $69.10   $69.10  
  7 purchase totals = $702.60       $772.3551   $772.34   $772.35   $772.30