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	$224.48	11.795%	$250.9574	$250.96	$250.95	$251.00
Purchase #2	$152.50	5.381%	$160.706	$160.71	$160.70	$160.70
Purchase #3	$17.89	4.369%	$18.6716	$18.67	$18.65	$18.70
Purchase #4	$74.40	7.745%	$80.1623	$80.16	$80.15	$80.20
Purchase #5	$72.83	13.575%	$82.7167	$82.72	$82.70	$82.70
Purchase #6	$171.55	10.418%	$189.4221	$189.42	$189.40	$189.40
Purchase #7	$222.66	3.623%	$230.727	$230.73	$230.75	$230.70
7 purchase totals =	$936.31		$1,013.3631	$1,013.37	$1,013.30	$1,013.40