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	$92.78	7.667%	$99.8934	$99.89	$99.90	$99.90
Purchase #2	$122.74	4.539%	$128.3112	$128.31	$128.30	$128.30
Purchase #3	$237.92	11.247%	$264.6789	$264.68	$264.70	$264.70
Purchase #4	$235.41	8.137%	$254.5653	$254.57	$254.55	$254.60
Purchase #5	$82.45	9.811%	$90.5392	$90.54	$90.55	$90.50
Purchase #6	$114.68	5.873%	$121.4152	$121.42	$121.40	$121.40
Purchase #7	$250.39	5.480%	$264.1114	$264.11	$264.10	$264.10
7 purchase totals =	$1,136.37		$1,223.5146	$1,223.52	$1,223.50	$1,223.50