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 $67.35   4.791%   $70.5767   $70.58   $70.60   $70.60  
  Purchase #2 $125.68   8.237%   $136.0323   $136.03   $136.05   $136.00  
  Purchase #3 $39.95   9.538%   $43.7604   $43.76   $43.75   $43.80  
  Purchase #4 $79.45   3.130%   $81.9368   $81.94   $81.95   $81.90  
  Purchase #5 $177.76   4.233%   $185.2846   $185.28   $185.30   $185.30  
  Purchase #6 $151.83   4.713%   $158.9857   $158.99   $159.00   $159.00  
  Purchase #7 $208.25   8.122%   $225.1641   $225.16   $225.15   $225.20  
  7 purchase totals = $850.27       $901.7406   $901.74   $901.80   $901.80