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	$142.39	12.580%	$160.3027	$160.30	$160.30	$160.30
Purchase #2	$151.32	7.390%	$162.5025	$162.50	$162.50	$162.50
Purchase #3	$238.86	4.627%	$249.9121	$249.91	$249.90	$249.90
Purchase #4	$24.74	13.795%	$28.1529	$28.15	$28.15	$28.20
Purchase #5	$138.45	3.556%	$143.3733	$143.37	$143.35	$143.40
Purchase #6	$19.30	11.385%	$21.4973	$21.50	$21.50	$21.50
Purchase #7	$250.26	11.732%	$279.6205	$279.62	$279.60	$279.60
7 purchase totals =	$965.32		$1,045.3613	$1,045.35	$1,045.30	$1,045.40