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	$79.61	4.542%	$83.2259	$83.23	$83.25	$83.20
Purchase #2	$136.89	10.568%	$151.3565	$151.36	$151.35	$151.40
Purchase #3	$153.81	3.324%	$158.9226	$158.92	$158.90	$158.90
Purchase #4	$103.65	7.561%	$111.487	$111.49	$111.50	$111.50
Purchase #5	$218.62	12.869%	$246.7542	$246.75	$246.75	$246.80
Purchase #6	$19.43	3.245%	$20.0605	$20.06	$20.05	$20.10
Purchase #7	$130.91	13.860%	$149.0541	$149.05	$149.05	$149.10
7 purchase totals =	$842.92		$920.8608	$920.86	$920.85	$921.00