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	$22.52	8.181%	$24.3624	$24.36	$24.35	$24.40
Purchase #2	$38.96	11.546%	$43.4583	$43.46	$43.45	$43.50
Purchase #3	$75.97	12.646%	$85.5772	$85.58	$85.60	$85.60
Purchase #4	$66.52	5.334%	$70.0682	$70.07	$70.05	$70.10
Purchase #5	$176.94	4.744%	$185.334	$185.33	$185.35	$185.30
Purchase #6	$94.33	11.508%	$105.1855	$105.19	$105.20	$105.20
Purchase #7	$113.92	12.278%	$127.9071	$127.91	$127.90	$127.90
7 purchase totals =	$589.16		$641.8927	$641.90	$641.90	$642.00