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	$102.39	3.197%	$105.6634	$105.66	$105.65	$105.70
Purchase #2	$48.65	9.530%	$53.2863	$53.29	$53.30	$53.30
Purchase #3	$59.72	9.856%	$65.606	$65.61	$65.60	$65.60
Purchase #4	$234.78	11.359%	$261.4487	$261.45	$261.45	$261.40
Purchase #5	$109.96	5.167%	$115.6416	$115.64	$115.65	$115.60
Purchase #6	$144.87	13.870%	$164.9635	$164.96	$164.95	$165.00
Purchase #7	$46.75	12.655%	$52.6662	$52.67	$52.65	$52.70
7 purchase totals =	$747.12		$819.2757	$819.28	$819.25	$819.30