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	$105.50	12.146%	$118.314	$118.31	$118.30	$118.30
Purchase #2	$74.94	13.581%	$85.1176	$85.12	$85.10	$85.10
Purchase #3	$119.93	5.466%	$126.4854	$126.49	$126.50	$126.50
Purchase #4	$32.91	10.447%	$36.3481	$36.35	$36.35	$36.30
Purchase #5	$212.84	4.500%	$222.4178	$222.42	$222.40	$222.40
Purchase #6	$26.30	7.592%	$28.2967	$28.30	$28.30	$28.30
Purchase #7	$158.54	13.561%	$180.0396	$180.04	$180.05	$180.00
7 purchase totals =	$730.96		$797.0192	$797.03	$797.00	$796.90