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 $76.88   8.758%   $83.6132   $83.61   $83.60   $83.60  
  Purchase #2 $214.74   4.582%   $224.5794   $224.58   $224.60   $224.60  
  Purchase #3 $20.30   11.144%   $22.5622   $22.56   $22.55   $22.60  
  Purchase #4 $94.28   7.795%   $101.6291   $101.63   $101.65   $101.60  
  Purchase #5 $46.35   3.621%   $48.0283   $48.03   $48.05   $48.00  
  Purchase #6 $224.67   8.720%   $244.2612   $244.26   $244.25   $244.30  
  Purchase #7 $116.64   9.303%   $127.491   $127.49   $127.50   $127.50  
  7 purchase totals = $793.86       $852.1644   $852.16   $852.20   $852.20