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	$103.76	5.438%	$109.4025	$109.40	$109.40	$109.40
Purchase #2	$52.45	4.674%	$54.9015	$54.90	$54.90	$54.90
Purchase #3	$22.51	13.685%	$25.5905	$25.59	$25.60	$25.60
Purchase #4	$138.82	5.856%	$146.9493	$146.95	$146.95	$146.90
Purchase #5	$209.50	11.823%	$234.2692	$234.27	$234.25	$234.30
Purchase #6	$172.74	8.348%	$187.1603	$187.16	$187.15	$187.20
Purchase #7	$127.69	3.242%	$131.8297	$131.83	$131.85	$131.80
7 purchase totals =	$827.47		$890.1030	$890.10	$890.10	$890.10