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 $85.35   11.819%   $95.4375   $95.44   $95.45   $95.40  
  Purchase #2 $67.38   13.393%   $76.4042   $76.40   $76.40   $76.40  
  Purchase #3 $150.57   8.694%   $163.6606   $163.66   $163.65   $163.70  
  Purchase #4 $186.64   3.741%   $193.6222   $193.62   $193.60   $193.60  
  Purchase #5 $8.72   11.308%   $9.7061   $9.71   $9.70   $9.70  
  Purchase #6 $213.86   10.718%   $236.7815   $236.78   $236.80   $236.80  
  Purchase #7 $195.50   12.825%   $220.5729   $220.57   $220.55   $220.60  
  7 purchase totals = $908.02       $996.1850   $996.18   $996.15   $996.20