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	$79.70	11.687%	$89.0145	$89.01	$89.00	$89.00
Purchase #2	$102.87	9.583%	$112.728	$112.73	$112.75	$112.70
Purchase #3	$133.65	7.785%	$144.0547	$144.05	$144.05	$144.10
Purchase #4	$81.89	8.874%	$89.1569	$89.16	$89.15	$89.20
Purchase #5	$175.86	13.397%	$199.42	$199.42	$199.40	$199.40
Purchase #6	$113.26	13.529%	$128.5829	$128.58	$128.60	$128.60
Purchase #7	$204.58	11.606%	$228.3236	$228.32	$228.30	$228.30
7 purchase totals =	$891.81		$991.2806	$991.27	$991.25	$991.30