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	$79.34	13.149%	$89.7724	$89.77	$89.75	$89.80
Purchase #2	$109.97	3.136%	$113.4187	$113.42	$113.40	$113.40
Purchase #3	$40.70	8.871%	$44.3105	$44.31	$44.30	$44.30
Purchase #4	$64.44	12.325%	$72.3822	$72.38	$72.40	$72.40
Purchase #5	$7.81	3.420%	$8.0771	$8.08	$8.10	$8.10
Purchase #6	$68.94	5.365%	$72.6386	$72.64	$72.65	$72.60
Purchase #7	$12.27	4.304%	$12.7981	$12.80	$12.80	$12.80
7 purchase totals =	$383.47		$413.3976	$413.40	$413.40	$413.40