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	$229.77	11.598%	$256.4187	$256.42	$256.40	$256.40
Purchase #2	$149.97	13.856%	$170.7498	$170.75	$170.75	$170.70
Purchase #3	$243.37	4.297%	$253.8276	$253.83	$253.85	$253.80
Purchase #4	$57.91	12.708%	$65.2692	$65.27	$65.25	$65.30
Purchase #5	$240.45	4.137%	$250.3974	$250.40	$250.40	$250.40
Purchase #6	$134.53	4.440%	$140.5031	$140.50	$140.50	$140.50
Purchase #7	$103.46	12.873%	$116.7784	$116.78	$116.80	$116.80
7 purchase totals =	$1,159.46		$1,253.9442	$1,253.95	$1,253.95	$1,253.90