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	$37.51	10.690%	$41.5198	$41.52	$41.50	$41.50
Purchase #2	$34.37	8.873%	$37.4197	$37.42	$37.40	$37.40
Purchase #3	$70.65	5.779%	$74.7329	$74.73	$74.75	$74.70
Purchase #4	$214.39	12.165%	$240.4705	$240.47	$240.45	$240.50
Purchase #5	$52.82	6.846%	$56.4361	$56.44	$56.45	$56.40
Purchase #6	$71.99	7.693%	$77.5282	$77.53	$77.55	$77.50
Purchase #7	$50.32	11.627%	$56.1707	$56.17	$56.15	$56.20
7 purchase totals =	$532.05		$584.2779	$584.28	$584.25	$584.20