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	$237.36	12.698%	$267.5	$267.50	$267.50	$267.50
Purchase #2	$130.75	4.485%	$136.6141	$136.61	$136.60	$136.60
Purchase #3	$43.61	10.160%	$48.0408	$48.04	$48.05	$48.00
Purchase #4	$220.94	5.521%	$233.1381	$233.14	$233.15	$233.10
Purchase #5	$135.79	10.781%	$150.4295	$150.43	$150.45	$150.40
Purchase #6	$158.82	12.356%	$178.4438	$178.44	$178.45	$178.40
Purchase #7	$135.42	12.649%	$152.5493	$152.55	$152.55	$152.50
7 purchase totals =	$1,062.69		$1,166.7156	$1,166.71	$1,166.75	$1,166.50