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	$22.39	4.444%	$23.385	$23.39	$23.40	$23.40
Purchase #2	$231.95	3.827%	$240.8267	$240.83	$240.85	$240.80
Purchase #3	$188.71	12.787%	$212.8403	$212.84	$212.85	$212.80
Purchase #4	$190.63	12.600%	$214.6494	$214.65	$214.65	$214.60
Purchase #5	$126.79	10.102%	$139.5983	$139.60	$139.60	$139.60
Purchase #6	$118.36	7.662%	$127.4287	$127.43	$127.45	$127.40
Purchase #7	$116.54	9.683%	$127.8246	$127.82	$127.80	$127.80
7 purchase totals =	$995.37		$1,086.5530	$1,086.56	$1,086.60	$1,086.40