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 $69.27   5.680%   $73.2045   $73.20   $73.20   $73.20  
  Purchase #2 $192.93   8.272%   $208.8892   $208.89   $208.90   $208.90  
  Purchase #3 $75.34   10.640%   $83.3562   $83.36   $83.35   $83.40  
  Purchase #4 $85.37   5.316%   $89.9083   $89.91   $89.90   $89.90  
  Purchase #5 $247.64   7.525%   $266.2749   $266.27   $266.25   $266.30  
  Purchase #6 $226.35   9.859%   $248.6658   $248.67   $248.65   $248.70  
  Purchase #7 $160.91   4.741%   $168.5387   $168.54   $168.55   $168.50  
  7 purchase totals = $1,057.81       $1,138.8376   $1,138.84   $1,138.80   $1,138.90