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	$19.31	6.332%	$20.5327	$20.53	$20.55	$20.50
Purchase #2	$223.69	13.277%	$253.3893	$253.39	$253.40	$253.40
Purchase #3	$77.52	10.268%	$85.4798	$85.48	$85.50	$85.50
Purchase #4	$21.75	9.403%	$23.7952	$23.80	$23.80	$23.80
Purchase #5	$36.37	4.299%	$37.9335	$37.93	$37.95	$37.90
Purchase #6	$48.60	5.579%	$51.3114	$51.31	$51.30	$51.30
Purchase #7	$190.59	13.231%	$215.807	$215.81	$215.80	$215.80
7 purchase totals =	$617.83		$688.2489	$688.25	$688.30	$688.20