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	$192.47	8.539%	$208.905	$208.91	$208.90	$208.90
Purchase #2	$173.68	3.805%	$180.2885	$180.29	$180.30	$180.30
Purchase #3	$89.79	5.187%	$94.4474	$94.45	$94.45	$94.40
Purchase #4	$172.83	4.559%	$180.7093	$180.71	$180.70	$180.70
Purchase #5	$48.89	5.103%	$51.3849	$51.38	$51.40	$51.40
Purchase #6	$239.45	6.269%	$254.4611	$254.46	$254.45	$254.50
Purchase #7	$182.93	3.286%	$188.9411	$188.94	$188.95	$188.90
7 purchase totals =	$1,100.04		$1,159.1373	$1,159.14	$1,159.15	$1,159.10