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	$207.95	9.874%	$228.483	$228.48	$228.50	$228.50
Purchase #2	$97.78	13.534%	$111.0135	$111.01	$111.00	$111.00
Purchase #3	$88.76	13.168%	$100.4479	$100.45	$100.45	$100.40
Purchase #4	$117.77	10.797%	$130.4856	$130.49	$130.50	$130.50
Purchase #5	$81.84	8.146%	$88.5067	$88.51	$88.50	$88.50
Purchase #6	$124.73	7.637%	$134.2556	$134.26	$134.25	$134.30
Purchase #7	$11.84	3.523%	$12.2571	$12.26	$12.25	$12.30
7 purchase totals =	$730.67		$805.4494	$805.46	$805.45	$805.50