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	$16.55	4.577%	$17.3075	$17.31	$17.30	$17.30
Purchase #2	$45.94	4.753%	$48.1235	$48.12	$48.10	$48.10
Purchase #3	$102.32	7.363%	$109.8538	$109.85	$109.85	$109.90
Purchase #4	$155.36	10.170%	$171.1601	$171.16	$171.15	$171.20
Purchase #5	$142.29	8.209%	$153.9706	$153.97	$153.95	$154.00
Purchase #6	$29.83	6.258%	$31.6968	$31.70	$31.70	$31.70
Purchase #7	$63.60	13.551%	$72.2184	$72.22	$72.20	$72.20
7 purchase totals =	$555.89		$604.3307	$604.33	$604.25	$604.40