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	$106.59	11.689%	$119.0493	$119.05	$119.05	$119.00
Purchase #2	$57.82	12.698%	$65.162	$65.16	$65.15	$65.20
Purchase #3	$76.59	3.724%	$79.4422	$79.44	$79.45	$79.40
Purchase #4	$141.49	8.329%	$153.2747	$153.27	$153.25	$153.30
Purchase #5	$144.67	9.436%	$158.3211	$158.32	$158.30	$158.30
Purchase #6	$24.40	3.859%	$25.3416	$25.34	$25.35	$25.30
Purchase #7	$38.29	10.518%	$42.3173	$42.32	$42.30	$42.30
7 purchase totals =	$589.85		$642.9082	$642.90	$642.85	$642.80