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	$179.30	10.733%	$198.5443	$198.54	$198.55	$198.50
Purchase #2	$233.77	10.328%	$257.9138	$257.91	$257.90	$257.90
Purchase #3	$235.48	9.667%	$258.2439	$258.24	$258.25	$258.20
Purchase #4	$81.62	4.619%	$85.39	$85.39	$85.40	$85.40
Purchase #5	$192.52	3.674%	$199.5932	$199.59	$199.60	$199.60
Purchase #6	$96.27	8.592%	$104.5415	$104.54	$104.55	$104.50
Purchase #7	$60.35	9.721%	$66.2166	$66.22	$66.20	$66.20
7 purchase totals =	$1,079.31		$1,170.4433	$1,170.43	$1,170.45	$1,170.30