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	$61.61	6.318%	$65.5025	$65.50	$65.50	$65.50
Purchase #2	$53.82	5.283%	$56.6633	$56.66	$56.65	$56.70
Purchase #3	$50.56	10.391%	$55.8137	$55.81	$55.80	$55.80
Purchase #4	$48.30	12.244%	$54.2139	$54.21	$54.20	$54.20
Purchase #5	$48.74	13.288%	$55.2166	$55.22	$55.20	$55.20
Purchase #6	$150.71	3.594%	$156.1265	$156.13	$156.15	$156.10
Purchase #7	$154.48	4.783%	$161.8688	$161.87	$161.85	$161.90
7 purchase totals =	$568.22		$605.4053	$605.40	$605.35	$605.40