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	$70.52	7.140%	$75.5551	$75.56	$75.55	$75.60
Purchase #2	$143.86	5.163%	$151.2875	$151.29	$151.30	$151.30
Purchase #3	$74.50	4.546%	$77.8868	$77.89	$77.90	$77.90
Purchase #4	$71.69	13.426%	$81.3151	$81.32	$81.30	$81.30
Purchase #5	$134.87	3.107%	$139.0604	$139.06	$139.05	$139.10
Purchase #6	$47.67	11.748%	$53.2703	$53.27	$53.25	$53.30
Purchase #7	$237.93	7.649%	$256.1293	$256.13	$256.15	$256.10
7 purchase totals =	$781.04		$834.5045	$834.52	$834.50	$834.60