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	$17.39	8.827%	$18.925	$18.93	$18.95	$18.90
Purchase #2	$230.89	13.808%	$262.7713	$262.77	$262.75	$262.80
Purchase #3	$143.30	13.412%	$162.5194	$162.52	$162.50	$162.50
Purchase #4	$60.29	3.824%	$62.5955	$62.60	$62.60	$62.60
Purchase #5	$186.78	5.463%	$196.9838	$196.98	$197.00	$197.00
Purchase #6	$39.73	4.826%	$41.6474	$41.65	$41.65	$41.60
Purchase #7	$153.66	3.629%	$159.2363	$159.24	$159.25	$159.20
7 purchase totals =	$832.04		$904.6787	$904.69	$904.70	$904.60