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	$238.30	7.176%	$255.4004	$255.40	$255.40	$255.40
Purchase #2	$151.43	7.360%	$162.5752	$162.58	$162.60	$162.60
Purchase #3	$26.92	3.517%	$27.8668	$27.87	$27.85	$27.90
Purchase #4	$88.42	4.138%	$92.0788	$92.08	$92.10	$92.10
Purchase #5	$133.51	10.131%	$147.0359	$147.04	$147.05	$147.00
Purchase #6	$60.32	9.846%	$66.2591	$66.26	$66.25	$66.30
Purchase #7	$78.77	11.772%	$88.0428	$88.04	$88.05	$88.00
7 purchase totals =	$777.67		$839.2590	$839.27	$839.30	$839.30