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	$120.82	7.189%	$129.5057	$129.51	$129.50	$129.50
Purchase #2	$111.97	13.812%	$127.4353	$127.44	$127.45	$127.40
Purchase #3	$73.80	3.594%	$76.4524	$76.45	$76.45	$76.50
Purchase #4	$246.75	3.473%	$255.3196	$255.32	$255.30	$255.30
Purchase #5	$158.61	5.575%	$167.4525	$167.45	$167.45	$167.50
Purchase #6	$30.60	11.379%	$34.082	$34.08	$34.10	$34.10
Purchase #7	$240.72	3.395%	$248.8924	$248.89	$248.90	$248.90
7 purchase totals =	$983.27		$1,039.1399	$1,039.14	$1,039.15	$1,039.20