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	$17.41	7.837%	$18.7744	$18.77	$18.75	$18.80
Purchase #2	$41.26	9.244%	$45.0741	$45.07	$45.05	$45.10
Purchase #3	$39.41	8.538%	$42.7748	$42.77	$42.75	$42.80
Purchase #4	$122.72	13.795%	$139.6492	$139.65	$139.65	$139.60
Purchase #5	$134.59	10.340%	$148.5066	$148.51	$148.50	$148.50
Purchase #6	$22.52	7.798%	$24.2761	$24.28	$24.30	$24.30
Purchase #7	$40.73	5.825%	$43.1025	$43.10	$43.10	$43.10
7 purchase totals =	$418.64		$462.1577	$462.15	$462.10	$462.20