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	$69.92	7.460%	$75.136	$75.14	$75.15	$75.10
Purchase #2	$151.31	10.242%	$166.8072	$166.81	$166.80	$166.80
Purchase #3	$73.83	9.278%	$80.6799	$80.68	$80.70	$80.70
Purchase #4	$55.34	7.389%	$59.4291	$59.43	$59.45	$59.40
Purchase #5	$184.72	8.440%	$200.3104	$200.31	$200.30	$200.30
Purchase #6	$41.47	13.773%	$47.1817	$47.18	$47.20	$47.20
Purchase #7	$111.72	13.199%	$126.4659	$126.47	$126.45	$126.50
7 purchase totals =	$688.31		$756.0102	$756.02	$756.05	$756.00