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	$52.79	12.145%	$59.2013	$59.20	$59.20	$59.20
Purchase #2	$181.96	4.195%	$189.5932	$189.59	$189.60	$189.60
Purchase #3	$137.51	12.831%	$155.1539	$155.15	$155.15	$155.20
Purchase #4	$20.43	11.315%	$22.7417	$22.74	$22.75	$22.70
Purchase #5	$250.55	12.226%	$281.1822	$281.18	$281.20	$281.20
Purchase #6	$182.62	8.869%	$198.8166	$198.82	$198.80	$198.80
Purchase #7	$42.92	5.545%	$45.2999	$45.30	$45.30	$45.30
7 purchase totals =	$868.78		$951.9888	$951.98	$952.00	$952.00