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	$204.54	10.847%	$226.7265	$226.73	$226.75	$226.70
Purchase #2	$141.43	3.130%	$145.8568	$145.86	$145.85	$145.90
Purchase #3	$60.34	10.416%	$66.625	$66.63	$66.65	$66.60
Purchase #4	$30.89	12.802%	$34.8445	$34.84	$34.85	$34.80
Purchase #5	$178.59	12.279%	$200.5191	$200.52	$200.50	$200.50
Purchase #6	$94.60	6.521%	$100.7689	$100.77	$100.75	$100.80
Purchase #7	$46.76	6.622%	$49.8564	$49.86	$49.85	$49.90
7 purchase totals =	$757.15		$825.1972	$825.21	$825.20	$825.20