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	$242.40	10.265%	$267.2824	$267.28	$267.30	$267.30
Purchase #2	$124.60	4.270%	$129.9204	$129.92	$129.90	$129.90
Purchase #3	$108.66	7.188%	$116.4705	$116.47	$116.45	$116.50
Purchase #4	$58.65	11.597%	$65.4516	$65.45	$65.45	$65.50
Purchase #5	$19.56	10.240%	$21.5629	$21.56	$21.55	$21.60
Purchase #6	$221.87	7.596%	$238.7232	$238.72	$238.70	$238.70
Purchase #7	$192.33	4.498%	$200.981	$200.98	$201.00	$201.00
7 purchase totals =	$968.07		$1,040.3920	$1,040.38	$1,040.35	$1,040.50