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	$124.81	12.620%	$140.561	$140.56	$140.55	$140.60
Purchase #2	$239.80	7.820%	$258.5524	$258.55	$258.55	$258.60
Purchase #3	$18.95	11.481%	$21.1256	$21.13	$21.15	$21.10
Purchase #4	$137.36	10.745%	$152.1193	$152.12	$152.10	$152.10
Purchase #5	$19.51	4.842%	$20.4547	$20.45	$20.45	$20.50
Purchase #6	$10.44	3.492%	$10.8046	$10.80	$10.80	$10.80
Purchase #7	$61.96	7.503%	$66.6089	$66.61	$66.60	$66.60
7 purchase totals =	$612.83		$670.2265	$670.22	$670.20	$670.30