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	$146.80	6.126%	$155.793	$155.79	$155.80	$155.80
Purchase #2	$105.30	13.557%	$119.5755	$119.58	$119.60	$119.60
Purchase #3	$245.77	3.607%	$254.6349	$254.63	$254.65	$254.60
Purchase #4	$227.46	4.743%	$238.2484	$238.25	$238.25	$238.20
Purchase #5	$210.72	12.719%	$237.5215	$237.52	$237.50	$237.50
Purchase #6	$143.61	5.830%	$151.9825	$151.98	$152.00	$152.00
Purchase #7	$37.41	13.382%	$42.4162	$42.42	$42.40	$42.40
7 purchase totals =	$1,117.07		$1,200.1720	$1,200.17	$1,200.20	$1,200.10