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	$166.61	4.162%	$173.5443	$173.54	$173.55	$173.50
Purchase #2	$131.72	11.234%	$146.5174	$146.52	$146.50	$146.50
Purchase #3	$153.27	6.202%	$162.7758	$162.78	$162.80	$162.80
Purchase #4	$136.35	3.109%	$140.5891	$140.59	$140.60	$140.60
Purchase #5	$62.84	5.751%	$66.4539	$66.45	$66.45	$66.50
Purchase #6	$31.78	13.194%	$35.9731	$35.97	$35.95	$36.00
Purchase #7	$139.41	5.177%	$146.6273	$146.63	$146.65	$146.60
7 purchase totals =	$821.98		$872.4809	$872.48	$872.50	$872.50