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	$72.98	9.608%	$79.9919	$79.99	$80.00	$80.00
Purchase #2	$99.37	5.183%	$104.5203	$104.52	$104.50	$104.50
Purchase #3	$57.45	4.389%	$59.9715	$59.97	$59.95	$60.00
Purchase #4	$99.67	4.649%	$104.3037	$104.30	$104.30	$104.30
Purchase #5	$202.37	6.450%	$215.4229	$215.42	$215.40	$215.40
Purchase #6	$235.78	7.761%	$254.0789	$254.08	$254.10	$254.10
Purchase #7	$139.99	13.290%	$158.5947	$158.59	$158.60	$158.60
7 purchase totals =	$907.61		$976.8839	$976.87	$976.85	$976.90