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	$149.68	4.318%	$156.1432	$156.14	$156.15	$156.10
Purchase #2	$22.49	8.788%	$24.4664	$24.47	$24.45	$24.50
Purchase #3	$206.96	13.507%	$234.9141	$234.91	$234.90	$234.90
Purchase #4	$161.81	12.622%	$182.2337	$182.23	$182.25	$182.20
Purchase #5	$47.29	12.294%	$53.1038	$53.10	$53.10	$53.10
Purchase #6	$175.93	11.828%	$196.739	$196.74	$196.75	$196.70
Purchase #7	$112.42	13.818%	$127.9542	$127.95	$127.95	$128.00
7 purchase totals =	$876.58		$975.5544	$975.54	$975.55	$975.50