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	$51.60	6.152%	$54.7744	$54.77	$54.75	$54.80
Purchase #2	$136.98	11.262%	$152.4067	$152.41	$152.40	$152.40
Purchase #3	$238.46	11.630%	$266.1929	$266.19	$266.20	$266.20
Purchase #4	$99.99	12.733%	$112.7217	$112.72	$112.70	$112.70
Purchase #5	$129.91	3.559%	$134.5335	$134.53	$134.55	$134.50
Purchase #6	$153.31	7.660%	$165.0535	$165.05	$165.05	$165.10
Purchase #7	$172.47	11.193%	$191.7746	$191.77	$191.75	$191.80
7 purchase totals =	$982.72		$1,077.4573	$1,077.44	$1,077.40	$1,077.50