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	$242.31	3.174%	$250.0009	$250.00	$250.00	$250.00
Purchase #2	$66.89	6.837%	$71.4633	$71.46	$71.45	$71.50
Purchase #3	$165.72	13.149%	$187.5105	$187.51	$187.50	$187.50
Purchase #4	$208.57	7.685%	$224.5986	$224.60	$224.60	$224.60
Purchase #5	$145.51	3.588%	$150.7309	$150.73	$150.75	$150.70
Purchase #6	$9.86	9.727%	$10.8191	$10.82	$10.80	$10.80
Purchase #7	$112.84	5.180%	$118.6851	$118.69	$118.70	$118.70
7 purchase totals =	$951.70		$1,013.8084	$1,013.81	$1,013.80	$1,013.80