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	$16.56	12.365%	$18.6076	$18.61	$18.60	$18.60
Purchase #2	$230.25	5.240%	$242.3151	$242.32	$242.30	$242.30
Purchase #3	$190.79	6.561%	$203.3077	$203.31	$203.30	$203.30
Purchase #4	$192.72	10.212%	$212.4006	$212.40	$212.40	$212.40
Purchase #5	$165.62	8.559%	$179.7954	$179.80	$179.80	$179.80
Purchase #6	$129.73	6.287%	$137.8861	$137.89	$137.90	$137.90
Purchase #7	$34.87	13.594%	$39.6102	$39.61	$39.60	$39.60
7 purchase totals =	$960.54		$1,033.9227	$1,033.94	$1,033.90	$1,033.90