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	$158.76	13.181%	$179.6862	$179.69	$179.70	$179.70
Purchase #2	$199.79	7.296%	$214.3667	$214.37	$214.35	$214.40
Purchase #3	$55.94	11.572%	$62.4134	$62.41	$62.40	$62.40
Purchase #4	$205.69	13.436%	$233.3265	$233.33	$233.35	$233.30
Purchase #5	$69.40	3.209%	$71.627	$71.63	$71.65	$71.60
Purchase #6	$5.40	3.265%	$5.5763	$5.58	$5.60	$5.60
Purchase #7	$88.68	12.599%	$99.8528	$99.85	$99.85	$99.90
7 purchase totals =	$783.66		$866.8489	$866.86	$866.90	$866.90