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	$92.29	8.554%	$100.1845	$100.18	$100.20	$100.20
Purchase #2	$244.64	7.154%	$262.1415	$262.14	$262.15	$262.10
Purchase #3	$217.93	12.806%	$245.8381	$245.84	$245.85	$245.80
Purchase #4	$36.77	5.802%	$38.9034	$38.90	$38.90	$38.90
Purchase #5	$60.26	9.711%	$66.1118	$66.11	$66.10	$66.10
Purchase #6	$131.73	9.416%	$144.1337	$144.13	$144.15	$144.10
Purchase #7	$126.82	12.187%	$142.2756	$142.28	$142.30	$142.30
7 purchase totals =	$910.44		$999.5886	$999.58	$999.65	$999.50