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	$88.29	12.374%	$99.215	$99.22	$99.20	$99.20
Purchase #2	$46.31	10.258%	$51.0605	$51.06	$51.05	$51.10
Purchase #3	$47.88	13.813%	$54.4937	$54.49	$54.50	$54.50
Purchase #4	$138.25	4.709%	$144.7602	$144.76	$144.75	$144.80
Purchase #5	$23.44	3.492%	$24.2585	$24.26	$24.25	$24.30
Purchase #6	$175.41	13.268%	$198.6834	$198.68	$198.70	$198.70
Purchase #7	$66.60	7.276%	$71.4458	$71.45	$71.45	$71.40
7 purchase totals =	$586.18		$643.9171	$643.92	$643.90	$644.00