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	$165.72	4.329%	$172.894	$172.89	$172.90	$172.90
Purchase #2	$6.58	3.269%	$6.7951	$6.80	$6.80	$6.80
Purchase #3	$108.89	8.263%	$117.8876	$117.89	$117.90	$117.90
Purchase #4	$177.71	12.206%	$199.4013	$199.40	$199.40	$199.40
Purchase #5	$114.51	11.110%	$127.2321	$127.23	$127.25	$127.20
Purchase #6	$197.80	12.126%	$221.7852	$221.79	$221.80	$221.80
Purchase #7	$59.29	10.293%	$65.3927	$65.39	$65.40	$65.40
7 purchase totals =	$830.50		$911.3880	$911.39	$911.45	$911.40