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	$35.56	11.203%	$39.5438	$39.54	$39.55	$39.50
Purchase #2	$62.56	5.777%	$66.1741	$66.17	$66.15	$66.20
Purchase #3	$47.63	6.616%	$50.7812	$50.78	$50.80	$50.80
Purchase #4	$139.55	4.647%	$146.0349	$146.03	$146.05	$146.00
Purchase #5	$52.60	5.178%	$55.3236	$55.32	$55.30	$55.30
Purchase #6	$124.72	13.539%	$141.6058	$141.61	$141.60	$141.60
Purchase #7	$248.35	8.405%	$269.2238	$269.22	$269.20	$269.20
7 purchase totals =	$710.97		$768.6872	$768.67	$768.65	$768.60