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	$128.28	13.144%	$145.1411	$145.14	$145.15	$145.10
Purchase #2	$34.62	10.129%	$38.1267	$38.13	$38.15	$38.10
Purchase #3	$39.83	7.370%	$42.7655	$42.77	$42.75	$42.80
Purchase #4	$113.66	3.822%	$118.0041	$118.00	$118.00	$118.00
Purchase #5	$131.79	9.584%	$144.4208	$144.42	$144.40	$144.40
Purchase #6	$189.91	5.720%	$200.7729	$200.77	$200.75	$200.80
Purchase #7	$48.32	9.478%	$52.8998	$52.90	$52.90	$52.90
7 purchase totals =	$686.41		$742.1309	$742.13	$742.10	$742.10