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	$73.68	12.207%	$82.6741	$82.67	$82.65	$82.70
Purchase #2	$68.60	4.562%	$71.7295	$71.73	$71.75	$71.70
Purchase #3	$52.94	12.254%	$59.4273	$59.43	$59.45	$59.40
Purchase #4	$52.76	13.698%	$59.9871	$59.99	$60.00	$60.00
Purchase #5	$223.38	13.536%	$253.6167	$253.62	$253.60	$253.60
Purchase #6	$146.39	13.554%	$166.2317	$166.23	$166.25	$166.20
Purchase #7	$123.46	10.530%	$136.4603	$136.46	$136.45	$136.50
7 purchase totals =	$741.21		$830.1267	$830.13	$830.15	$830.10