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 $85.42   12.389%   $96.0027   $96.00   $96.00   $96.00  
  Purchase #2 $24.45   8.531%   $26.5358   $26.54   $26.55   $26.50  
  Purchase #3 $234.53   13.285%   $265.6873   $265.69   $265.70   $265.70  
  Purchase #4 $233.60   3.501%   $241.7783   $241.78   $241.80   $241.80  
  Purchase #5 $115.72   12.802%   $130.5345   $130.53   $130.55   $130.50  
  Purchase #6 $169.71   5.420%   $178.9083   $178.91   $178.90   $178.90  
  Purchase #7 $201.51   3.625%   $208.8147   $208.81   $208.80   $208.80  
  7 purchase totals = $1,064.94       $1,148.2616   $1,148.26   $1,148.30   $1,148.20