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	$127.70	4.384%	$133.2984	$133.30	$133.30	$133.30
Purchase #2	$176.67	12.212%	$198.2449	$198.24	$198.25	$198.20
Purchase #3	$57.83	7.695%	$62.28	$62.28	$62.30	$62.30
Purchase #4	$19.45	4.874%	$20.398	$20.40	$20.40	$20.40
Purchase #5	$95.59	4.840%	$100.2166	$100.22	$100.20	$100.20
Purchase #6	$139.78	13.139%	$158.1457	$158.15	$158.15	$158.10
Purchase #7	$107.78	9.622%	$118.1506	$118.15	$118.15	$118.20
7 purchase totals =	$724.80		$790.7342	$790.74	$790.75	$790.70