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 $84.84   13.475%   $96.2722   $96.27   $96.25   $96.30  
  Purchase #2 $244.90   8.440%   $265.5696   $265.57   $265.55   $265.60  
  Purchase #3 $128.65   4.686%   $134.6785   $134.68   $134.70   $134.70  
  Purchase #4 $193.72   10.487%   $214.0354   $214.04   $214.05   $214.00  
  Purchase #5 $72.92   4.769%   $76.3976   $76.40   $76.40   $76.40  
  Purchase #6 $172.67   12.239%   $193.8031   $193.80   $193.80   $193.80  
  Purchase #7 $207.32   6.793%   $221.4032   $221.40   $221.40   $221.40  
  7 purchase totals = $1,105.02       $1,202.1596   $1,202.16   $1,202.15   $1,202.20