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	$53.29	4.469%	$55.6715	$55.67	$55.65	$55.70
Purchase #2	$121.49	10.171%	$133.8467	$133.85	$133.85	$133.80
Purchase #3	$50.30	8.398%	$54.5242	$54.52	$54.50	$54.50
Purchase #4	$218.86	9.739%	$240.1748	$240.17	$240.15	$240.20
Purchase #5	$48.90	12.869%	$55.1929	$55.19	$55.20	$55.20
Purchase #6	$215.66	5.864%	$228.3063	$228.31	$228.30	$228.30
Purchase #7	$133.80	13.224%	$151.4937	$151.49	$151.50	$151.50
7 purchase totals =	$842.30		$919.2101	$919.20	$919.15	$919.20