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	$162.78	6.845%	$173.9223	$173.92	$173.90	$173.90
Purchase #2	$37.63	13.591%	$42.7443	$42.74	$42.75	$42.70
Purchase #3	$135.26	10.578%	$149.5678	$149.57	$149.55	$149.60
Purchase #4	$182.41	7.247%	$195.6293	$195.63	$195.65	$195.60
Purchase #5	$89.32	12.535%	$100.5163	$100.52	$100.50	$100.50
Purchase #6	$70.79	3.251%	$73.0914	$73.09	$73.10	$73.10
Purchase #7	$84.93	6.173%	$90.1727	$90.17	$90.15	$90.20
7 purchase totals =	$763.12		$825.6441	$825.64	$825.60	$825.60