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 $214.48   13.264%   $242.9286   $242.93   $242.95   $242.90  
  Purchase #2 $208.36   5.499%   $219.8177   $219.82   $219.80   $219.80  
  Purchase #3 $73.54   3.698%   $76.2595   $76.26   $76.25   $76.30  
  Purchase #4 $213.64   5.714%   $225.8474   $225.85   $225.85   $225.80  
  Purchase #5 $224.52   12.194%   $251.898   $251.90   $251.90   $251.90  
  Purchase #6 $250.39   10.670%   $277.1066   $277.11   $277.10   $277.10  
  Purchase #7 $111.30   13.406%   $126.2209   $126.22   $126.20   $126.20  
  7 purchase totals = $1,296.23       $1,420.0787   $1,420.09   $1,420.05   $1,420.00