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	$87.30	13.464%	$99.0541	$99.05	$99.05	$99.10
Purchase #2	$114.36	7.660%	$123.12	$123.12	$123.10	$123.10
Purchase #3	$47.55	8.852%	$51.7591	$51.76	$51.75	$51.80
Purchase #4	$73.68	4.827%	$77.2365	$77.24	$77.25	$77.20
Purchase #5	$46.99	6.784%	$50.1778	$50.18	$50.20	$50.20
Purchase #6	$78.90	8.475%	$85.5868	$85.59	$85.60	$85.60
Purchase #7	$222.53	4.217%	$231.9141	$231.91	$231.90	$231.90
7 purchase totals =	$671.31		$718.8484	$718.85	$718.85	$718.90