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	$27.71	11.453%	$30.8836	$30.88	$30.90	$30.90
Purchase #2	$129.52	5.603%	$136.777	$136.78	$136.80	$136.80
Purchase #3	$39.85	4.260%	$41.5476	$41.55	$41.55	$41.50
Purchase #4	$15.75	5.366%	$16.5951	$16.60	$16.60	$16.60
Purchase #5	$111.92	10.742%	$123.9424	$123.94	$123.95	$123.90
Purchase #6	$9.25	11.425%	$10.3068	$10.31	$10.30	$10.30
Purchase #7	$186.51	5.563%	$196.8856	$196.89	$196.90	$196.90
7 purchase totals =	$520.51		$556.9381	$556.95	$557.00	$556.90