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	$6.70	10.183%	$7.3823	$7.38	$7.40	$7.40
Purchase #2	$116.42	10.213%	$128.31	$128.31	$128.30	$128.30
Purchase #3	$26.61	9.510%	$29.1406	$29.14	$29.15	$29.10
Purchase #4	$250.31	8.439%	$271.4337	$271.43	$271.45	$271.40
Purchase #5	$12.61	3.172%	$13.01	$13.01	$13.00	$13.00
Purchase #6	$131.94	12.229%	$148.0749	$148.07	$148.05	$148.10
Purchase #7	$74.93	7.123%	$80.2673	$80.27	$80.25	$80.30
7 purchase totals =	$619.52		$677.6188	$677.61	$677.60	$677.60