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	$86.31	9.229%	$94.2755	$94.28	$94.30	$94.30
Purchase #2	$145.83	3.409%	$150.8013	$150.80	$150.80	$150.80
Purchase #3	$103.68	7.213%	$111.1584	$111.16	$111.15	$111.20
Purchase #4	$153.80	7.669%	$165.5949	$165.59	$165.60	$165.60
Purchase #5	$49.48	4.487%	$51.7002	$51.70	$51.70	$51.70
Purchase #6	$210.43	5.490%	$221.9826	$221.98	$222.00	$222.00
Purchase #7	$7.51	5.602%	$7.9307	$7.93	$7.95	$7.90
7 purchase totals =	$757.04		$803.4436	$803.44	$803.50	$803.50