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	$236.83	7.798%	$255.298	$255.30	$255.30	$255.30
Purchase #2	$118.93	10.191%	$131.0502	$131.05	$131.05	$131.10
Purchase #3	$244.92	13.798%	$278.7141	$278.71	$278.70	$278.70
Purchase #4	$40.30	13.754%	$45.8429	$45.84	$45.85	$45.80
Purchase #5	$99.51	10.342%	$109.8013	$109.80	$109.80	$109.80
Purchase #6	$241.41	6.304%	$256.6285	$256.63	$256.65	$256.60
Purchase #7	$125.68	7.178%	$134.7013	$134.70	$134.70	$134.70
7 purchase totals =	$1,107.58		$1,212.0363	$1,212.03	$1,212.05	$1,212.00