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	$31.41	12.422%	$35.3118	$35.31	$35.30	$35.30
Purchase #2	$176.80	12.323%	$198.5871	$198.59	$198.60	$198.60
Purchase #3	$128.68	12.598%	$144.8911	$144.89	$144.90	$144.90
Purchase #4	$96.90	13.324%	$109.811	$109.81	$109.80	$109.80
Purchase #5	$28.64	4.227%	$29.8506	$29.85	$29.85	$29.90
Purchase #6	$226.89	12.797%	$255.9251	$255.93	$255.95	$255.90
Purchase #7	$20.92	6.608%	$22.3024	$22.30	$22.30	$22.30
7 purchase totals =	$710.24		$796.6791	$796.68	$796.70	$796.70