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	$248.34	5.792%	$262.7239	$262.72	$262.70	$262.70
Purchase #2	$138.33	9.723%	$151.7798	$151.78	$151.80	$151.80
Purchase #3	$155.78	6.480%	$165.8745	$165.87	$165.85	$165.90
Purchase #4	$170.33	7.667%	$183.3892	$183.39	$183.40	$183.40
Purchase #5	$238.38	6.806%	$254.6041	$254.60	$254.60	$254.60
Purchase #6	$79.62	9.685%	$87.3312	$87.33	$87.35	$87.30
Purchase #7	$207.47	4.334%	$216.4617	$216.46	$216.45	$216.50
7 purchase totals =	$1,238.25		$1,322.1644	$1,322.15	$1,322.15	$1,322.20