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	$69.76	13.818%	$79.3994	$79.40	$79.40	$79.40
Purchase #2	$118.99	13.232%	$134.7348	$134.73	$134.75	$134.70
Purchase #3	$137.46	11.638%	$153.4576	$153.46	$153.45	$153.50
Purchase #4	$223.87	12.230%	$251.2493	$251.25	$251.25	$251.20
Purchase #5	$151.59	10.481%	$167.4781	$167.48	$167.50	$167.50
Purchase #6	$209.43	11.546%	$233.6108	$233.61	$233.60	$233.60
Purchase #7	$94.62	6.395%	$100.6709	$100.67	$100.65	$100.70
7 purchase totals =	$1,005.72		$1,120.6009	$1,120.60	$1,120.60	$1,120.60