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	$138.87	11.675%	$155.0831	$155.08	$155.10	$155.10
Purchase #2	$158.90	12.496%	$178.7561	$178.76	$178.75	$178.80
Purchase #3	$97.71	12.151%	$109.5827	$109.58	$109.60	$109.60
Purchase #4	$45.87	5.277%	$48.2906	$48.29	$48.30	$48.30
Purchase #5	$222.70	10.722%	$246.5779	$246.58	$246.60	$246.60
Purchase #6	$146.32	10.839%	$162.1796	$162.18	$162.20	$162.20
Purchase #7	$167.91	9.573%	$183.984	$183.98	$184.00	$184.00
7 purchase totals =	$978.28		$1,084.4540	$1,084.45	$1,084.55	$1,084.60