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	$70.55	6.149%	$74.8881	$74.89	$74.90	$74.90
Purchase #2	$36.35	3.494%	$37.6201	$37.62	$37.60	$37.60
Purchase #3	$76.85	6.135%	$81.5647	$81.56	$81.55	$81.60
Purchase #4	$82.60	7.788%	$89.0329	$89.03	$89.05	$89.00
Purchase #5	$54.28	6.199%	$57.6448	$57.64	$57.65	$57.60
Purchase #6	$188.48	5.653%	$199.1348	$199.13	$199.15	$199.10
Purchase #7	$226.48	5.328%	$238.5469	$238.55	$238.55	$238.50
7 purchase totals =	$735.59		$778.4323	$778.42	$778.45	$778.30