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	$233.51	9.535%	$255.7752	$255.78	$255.80	$255.80
Purchase #2	$13.58	10.720%	$15.0358	$15.04	$15.05	$15.00
Purchase #3	$131.92	6.775%	$140.8576	$140.86	$140.85	$140.90
Purchase #4	$249.82	9.251%	$272.9308	$272.93	$272.95	$272.90
Purchase #5	$85.42	6.344%	$90.839	$90.84	$90.85	$90.80
Purchase #6	$185.95	3.704%	$192.8376	$192.84	$192.85	$192.80
Purchase #7	$26.52	7.833%	$28.5973	$28.60	$28.60	$28.60
7 purchase totals =	$926.72		$996.8733	$996.89	$996.95	$996.80