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	$90.53	10.534%	$100.0664	$100.07	$100.05	$100.10
Purchase #2	$234.81	7.417%	$252.2259	$252.23	$252.25	$252.20
Purchase #3	$62.40	13.538%	$70.8477	$70.85	$70.85	$70.80
Purchase #4	$75.89	4.119%	$79.0159	$79.02	$79.00	$79.00
Purchase #5	$188.30	10.225%	$207.5537	$207.55	$207.55	$207.60
Purchase #6	$151.31	10.422%	$167.0795	$167.08	$167.10	$167.10
Purchase #7	$236.32	7.739%	$254.6088	$254.61	$254.60	$254.60
7 purchase totals =	$1,039.56		$1,131.3979	$1,131.41	$1,131.40	$1,131.40