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	$77.25	5.440%	$81.4524	$81.45	$81.45	$81.50
Purchase #2	$147.33	4.367%	$153.7639	$153.76	$153.75	$153.80
Purchase #3	$39.89	11.272%	$44.3864	$44.39	$44.40	$44.40
Purchase #4	$159.87	3.483%	$165.4383	$165.44	$165.45	$165.40
Purchase #5	$116.39	9.631%	$127.5995	$127.60	$127.60	$127.60
Purchase #6	$159.25	8.510%	$172.8022	$172.80	$172.80	$172.80
Purchase #7	$51.77	11.292%	$57.6159	$57.62	$57.60	$57.60
7 purchase totals =	$751.75		$803.0586	$803.06	$803.05	$803.10