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	$13.93	12.212%	$15.6311	$15.63	$15.65	$15.60
Purchase #2	$64.35	4.685%	$67.3648	$67.36	$67.35	$67.40
Purchase #3	$173.67	13.281%	$196.7351	$196.74	$196.75	$196.70
Purchase #4	$215.25	11.265%	$239.4979	$239.50	$239.50	$239.50
Purchase #5	$136.98	10.440%	$151.2807	$151.28	$151.30	$151.30
Purchase #6	$59.73	13.573%	$67.8372	$67.84	$67.85	$67.80
Purchase #7	$145.79	9.733%	$159.9797	$159.98	$160.00	$160.00
7 purchase totals =	$809.70		$898.3265	$898.33	$898.40	$898.30