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	$222.70	4.663%	$233.0845	$233.08	$233.10	$233.10
Purchase #2	$186.74	12.786%	$210.6166	$210.62	$210.60	$210.60
Purchase #3	$100.98	10.655%	$111.7394	$111.74	$111.75	$111.70
Purchase #4	$17.72	6.268%	$18.8307	$18.83	$18.85	$18.80
Purchase #5	$69.68	12.379%	$78.3057	$78.31	$78.30	$78.30
Purchase #6	$201.66	9.353%	$220.5213	$220.52	$220.50	$220.50
Purchase #7	$106.76	9.787%	$117.2086	$117.21	$117.20	$117.20
7 purchase totals =	$906.24		$990.3068	$990.31	$990.30	$990.20