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	$112.41	13.317%	$127.3796	$127.38	$127.40	$127.40
Purchase #2	$69.77	8.146%	$75.4535	$75.45	$75.45	$75.50
Purchase #3	$58.50	11.802%	$65.4042	$65.40	$65.40	$65.40
Purchase #4	$59.25	9.523%	$64.8924	$64.89	$64.90	$64.90
Purchase #5	$140.40	13.144%	$158.8542	$158.85	$158.85	$158.90
Purchase #6	$159.33	9.330%	$174.1955	$174.20	$174.20	$174.20
Purchase #7	$207.95	8.201%	$225.004	$225.00	$225.00	$225.00
7 purchase totals =	$807.61		$891.1834	$891.17	$891.20	$891.30