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	$47.48	13.161%	$53.7288	$53.73	$53.75	$53.70
Purchase #2	$29.71	9.426%	$32.5105	$32.51	$32.50	$32.50
Purchase #3	$153.54	3.762%	$159.3162	$159.32	$159.30	$159.30
Purchase #4	$165.54	4.457%	$172.9181	$172.92	$172.90	$172.90
Purchase #5	$114.90	13.160%	$130.0208	$130.02	$130.00	$130.00
Purchase #6	$105.32	6.618%	$112.2901	$112.29	$112.30	$112.30
Purchase #7	$65.25	6.840%	$69.7131	$69.71	$69.70	$69.70
7 purchase totals =	$681.74		$730.4976	$730.50	$730.45	$730.40