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	$65.51	10.696%	$72.5169	$72.52	$72.50	$72.50
Purchase #2	$98.38	7.475%	$105.7339	$105.73	$105.75	$105.70
Purchase #3	$240.45	4.422%	$251.0827	$251.08	$251.10	$251.10
Purchase #4	$81.93	10.419%	$90.4663	$90.47	$90.45	$90.50
Purchase #5	$30.72	6.318%	$32.6609	$32.66	$32.65	$32.70
Purchase #6	$13.43	7.448%	$14.4303	$14.43	$14.45	$14.40
Purchase #7	$17.33	5.688%	$18.3157	$18.32	$18.30	$18.30
7 purchase totals =	$547.75		$585.2067	$585.21	$585.20	$585.20