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	$48.94	7.274%	$52.4999	$52.50	$52.50	$52.50
Purchase #2	$240.76	4.844%	$252.4224	$252.42	$252.40	$252.40
Purchase #3	$129.56	13.243%	$146.7176	$146.72	$146.70	$146.70
Purchase #4	$85.34	5.866%	$90.346	$90.35	$90.35	$90.30
Purchase #5	$192.87	3.342%	$199.3157	$199.32	$199.30	$199.30
Purchase #6	$40.79	7.534%	$43.8631	$43.86	$43.85	$43.90
Purchase #7	$156.65	7.820%	$168.9	$168.90	$168.90	$168.90
7 purchase totals =	$894.91		$954.0647	$954.07	$954.00	$954.00