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	$68.72	12.106%	$77.0392	$77.04	$77.05	$77.00
Purchase #2	$105.56	13.871%	$120.2022	$120.20	$120.20	$120.20
Purchase #3	$40.58	13.773%	$46.1691	$46.17	$46.15	$46.20
Purchase #4	$119.79	5.398%	$126.2563	$126.26	$126.25	$126.30
Purchase #5	$101.34	4.572%	$105.9733	$105.97	$105.95	$106.00
Purchase #6	$90.29	11.659%	$100.8169	$100.82	$100.80	$100.80
Purchase #7	$152.53	12.197%	$171.1341	$171.13	$171.15	$171.10
7 purchase totals =	$678.81		$747.5911	$747.59	$747.55	$747.60