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	$224.72	11.420%	$250.383	$250.38	$250.40	$250.40
Purchase #2	$188.46	13.587%	$214.0661	$214.07	$214.05	$214.10
Purchase #3	$94.42	9.533%	$103.4211	$103.42	$103.40	$103.40
Purchase #4	$158.34	12.111%	$177.5166	$177.52	$177.50	$177.50
Purchase #5	$6.56	3.650%	$6.7994	$6.80	$6.80	$6.80
Purchase #6	$18.84	6.224%	$20.0126	$20.01	$20.00	$20.00
Purchase #7	$40.83	6.246%	$43.3802	$43.38	$43.40	$43.40
7 purchase totals =	$732.17		$815.5790	$815.58	$815.55	$815.60