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	$38.35	6.633%	$40.8938	$40.89	$40.90	$40.90
Purchase #2	$132.87	4.146%	$138.3788	$138.38	$138.40	$138.40
Purchase #3	$250.82	11.145%	$278.7739	$278.77	$278.75	$278.80
Purchase #4	$195.38	11.676%	$218.1926	$218.19	$218.20	$218.20
Purchase #5	$246.32	8.208%	$266.5379	$266.54	$266.55	$266.50
Purchase #6	$43.82	10.551%	$48.4434	$48.44	$48.45	$48.40
Purchase #7	$164.31	10.454%	$181.487	$181.49	$181.50	$181.50
7 purchase totals =	$1,071.87		$1,172.7074	$1,172.70	$1,172.75	$1,172.70