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	$83.74	6.631%	$89.2928	$89.29	$89.30	$89.30
Purchase #2	$31.78	5.612%	$33.5635	$33.56	$33.55	$33.60
Purchase #3	$137.29	4.466%	$143.4214	$143.42	$143.40	$143.40
Purchase #4	$226.89	12.553%	$255.3715	$255.37	$255.35	$255.40
Purchase #5	$141.97	11.743%	$158.6415	$158.64	$158.65	$158.60
Purchase #6	$123.65	4.127%	$128.753	$128.75	$128.75	$128.80
Purchase #7	$78.64	12.215%	$88.2459	$88.25	$88.25	$88.20
7 purchase totals =	$823.96		$897.2896	$897.28	$897.25	$897.30