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	$224.33	6.173%	$238.1779	$238.18	$238.20	$238.20
Purchase #2	$105.75	11.840%	$118.2708	$118.27	$118.25	$118.30
Purchase #3	$22.41	10.268%	$24.7111	$24.71	$24.70	$24.70
Purchase #4	$53.37	3.599%	$55.2908	$55.29	$55.30	$55.30
Purchase #5	$8.28	3.854%	$8.5991	$8.60	$8.60	$8.60
Purchase #6	$151.71	4.654%	$158.7706	$158.77	$158.75	$158.80
Purchase #7	$84.84	7.131%	$90.8899	$90.89	$90.90	$90.90
7 purchase totals =	$650.69		$694.7102	$694.71	$694.70	$694.80