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	$50.67	8.465%	$54.9592	$54.96	$54.95	$55.00
Purchase #2	$175.74	13.360%	$199.2189	$199.22	$199.20	$199.20
Purchase #3	$30.98	4.185%	$32.2765	$32.28	$32.30	$32.30
Purchase #4	$10.89	6.773%	$11.6276	$11.63	$11.65	$11.60
Purchase #5	$234.52	6.493%	$249.7474	$249.75	$249.75	$249.70
Purchase #6	$13.52	13.863%	$15.3943	$15.39	$15.40	$15.40
Purchase #7	$67.71	7.140%	$72.5445	$72.54	$72.55	$72.50
7 purchase totals =	$584.03		$635.7684	$635.77	$635.80	$635.70