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	$138.89	8.128%	$150.179	$150.18	$150.20	$150.20
Purchase #2	$76.26	8.741%	$82.9259	$82.93	$82.95	$82.90
Purchase #3	$142.75	10.800%	$158.167	$158.17	$158.15	$158.20
Purchase #4	$100.81	4.133%	$104.9765	$104.98	$105.00	$105.00
Purchase #5	$153.59	3.263%	$158.6016	$158.60	$158.60	$158.60
Purchase #6	$231.52	11.487%	$258.1147	$258.11	$258.10	$258.10
Purchase #7	$27.43	6.486%	$29.2091	$29.21	$29.20	$29.20
7 purchase totals =	$871.25		$942.1738	$942.18	$942.20	$942.20