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	$165.78	3.779%	$172.0448	$172.04	$172.05	$172.00
Purchase #2	$166.63	13.666%	$189.4017	$189.40	$189.40	$189.40
Purchase #3	$31.88	5.733%	$33.7077	$33.71	$33.70	$33.70
Purchase #4	$18.92	4.243%	$19.7228	$19.72	$19.70	$19.70
Purchase #5	$6.66	11.305%	$7.4129	$7.41	$7.40	$7.40
Purchase #6	$9.70	9.683%	$10.6393	$10.64	$10.65	$10.60
Purchase #7	$190.26	13.297%	$215.5589	$215.56	$215.55	$215.60
7 purchase totals =	$589.83		$648.4881	$648.48	$648.45	$648.40