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	$50.90	4.413%	$53.1462	$53.15	$53.15	$53.10
Purchase #2	$180.80	9.429%	$197.8476	$197.85	$197.85	$197.80
Purchase #3	$100.65	10.477%	$111.1951	$111.20	$111.20	$111.20
Purchase #4	$104.88	4.667%	$109.7747	$109.77	$109.75	$109.80
Purchase #5	$169.48	5.466%	$178.7438	$178.74	$178.75	$178.70
Purchase #6	$143.99	5.497%	$151.9051	$151.91	$151.90	$151.90
Purchase #7	$36.71	3.443%	$37.9739	$37.97	$37.95	$38.00
7 purchase totals =	$787.41		$840.5864	$840.59	$840.55	$840.50