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	$136.73	3.173%	$141.0684	$141.07	$141.05	$141.10
Purchase #2	$155.65	8.237%	$168.4709	$168.47	$168.45	$168.50
Purchase #3	$152.77	4.646%	$159.8677	$159.87	$159.85	$159.90
Purchase #4	$62.80	4.792%	$65.8094	$65.81	$65.80	$65.80
Purchase #5	$160.35	8.438%	$173.8803	$173.88	$173.90	$173.90
Purchase #6	$46.25	13.416%	$52.4549	$52.45	$52.45	$52.50
Purchase #7	$50.82	13.149%	$57.5023	$57.50	$57.50	$57.50
7 purchase totals =	$765.37		$819.0539	$819.05	$819.00	$819.20