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	$104.38	7.753%	$112.4726	$112.47	$112.45	$112.50
Purchase #2	$225.25	12.546%	$253.5099	$253.51	$253.50	$253.50
Purchase #3	$11.76	3.123%	$12.1273	$12.13	$12.15	$12.10
Purchase #4	$53.56	4.200%	$55.8095	$55.81	$55.80	$55.80
Purchase #5	$175.65	9.413%	$192.1839	$192.18	$192.20	$192.20
Purchase #6	$146.62	4.250%	$152.8514	$152.85	$152.85	$152.90
Purchase #7	$77.61	12.547%	$87.3477	$87.35	$87.35	$87.30
7 purchase totals =	$794.83		$866.3023	$866.30	$866.30	$866.30