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	$139.26	13.683%	$158.3149	$158.31	$158.30	$158.30
Purchase #2	$200.85	3.202%	$207.2812	$207.28	$207.30	$207.30
Purchase #3	$174.48	7.588%	$187.7195	$187.72	$187.70	$187.70
Purchase #4	$46.94	3.345%	$48.5101	$48.51	$48.50	$48.50
Purchase #5	$130.90	11.124%	$145.4613	$145.46	$145.45	$145.50
Purchase #6	$103.71	7.236%	$111.2145	$111.21	$111.20	$111.20
Purchase #7	$130.50	6.852%	$139.4419	$139.44	$139.45	$139.40
7 purchase totals =	$926.64		$997.9434	$997.93	$997.90	$997.90