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	$118.87	13.857%	$135.3418	$135.34	$135.35	$135.30
Purchase #2	$99.73	11.627%	$111.3256	$111.33	$111.35	$111.30
Purchase #3	$45.35	10.758%	$50.2288	$50.23	$50.25	$50.20
Purchase #4	$92.50	11.649%	$103.2753	$103.28	$103.30	$103.30
Purchase #5	$194.83	10.142%	$214.5897	$214.59	$214.60	$214.60
Purchase #6	$104.97	4.420%	$109.6097	$109.61	$109.60	$109.60
Purchase #7	$118.61	3.295%	$122.5182	$122.52	$122.50	$122.50
7 purchase totals =	$774.86		$846.8891	$846.90	$846.95	$846.80