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	$159.59	12.406%	$179.3887	$179.39	$179.40	$179.40
Purchase #2	$108.90	5.731%	$115.1411	$115.14	$115.15	$115.10
Purchase #3	$138.39	8.575%	$150.2569	$150.26	$150.25	$150.30
Purchase #4	$138.27	11.301%	$153.8959	$153.90	$153.90	$153.90
Purchase #5	$47.41	10.436%	$52.3577	$52.36	$52.35	$52.40
Purchase #6	$103.34	12.809%	$116.5768	$116.58	$116.60	$116.60
Purchase #7	$223.65	11.377%	$249.0947	$249.09	$249.10	$249.10
7 purchase totals =	$919.55		$1,016.7118	$1,016.72	$1,016.75	$1,016.80