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	$34.58	10.507%	$38.2133	$38.21	$38.20	$38.20
Purchase #2	$213.52	9.724%	$234.2827	$234.28	$234.30	$234.30
Purchase #3	$19.62	4.575%	$20.5176	$20.52	$20.50	$20.50
Purchase #4	$112.57	13.314%	$127.5576	$127.56	$127.55	$127.60
Purchase #5	$190.52	7.192%	$204.2222	$204.22	$204.20	$204.20
Purchase #6	$32.45	6.200%	$34.4619	$34.46	$34.45	$34.50
Purchase #7	$27.62	13.271%	$31.2855	$31.29	$31.30	$31.30
7 purchase totals =	$630.88		$690.5408	$690.54	$690.50	$690.60