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	$40.73	4.169%	$42.428	$42.43	$42.45	$42.40
Purchase #2	$64.34	5.335%	$67.7725	$67.77	$67.75	$67.80
Purchase #3	$83.63	6.415%	$88.9949	$88.99	$89.00	$89.00
Purchase #4	$70.62	11.626%	$78.8303	$78.83	$78.85	$78.80
Purchase #5	$145.90	13.812%	$166.0517	$166.05	$166.05	$166.10
Purchase #6	$128.58	12.506%	$144.6602	$144.66	$144.65	$144.70
Purchase #7	$82.62	9.726%	$90.6556	$90.66	$90.65	$90.70
7 purchase totals =	$616.42		$679.3932	$679.39	$679.40	$679.50