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	$150.82	5.301%	$158.815	$158.82	$158.80	$158.80
Purchase #2	$167.95	9.504%	$183.912	$183.91	$183.90	$183.90
Purchase #3	$192.77	8.690%	$209.5217	$209.52	$209.50	$209.50
Purchase #4	$35.42	13.267%	$40.1192	$40.12	$40.10	$40.10
Purchase #5	$141.89	8.649%	$154.1621	$154.16	$154.15	$154.20
Purchase #6	$54.65	8.378%	$59.2286	$59.23	$59.25	$59.20
Purchase #7	$95.51	10.236%	$105.2864	$105.29	$105.30	$105.30
7 purchase totals =	$839.01		$911.0450	$911.05	$911.00	$911.00