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	$24.32	13.483%	$27.5991	$27.60	$27.60	$27.60
Purchase #2	$72.99	10.361%	$80.5525	$80.55	$80.55	$80.60
Purchase #3	$158.34	12.589%	$178.2734	$178.27	$178.25	$178.30
Purchase #4	$112.84	5.231%	$118.7427	$118.74	$118.75	$118.70
Purchase #5	$43.51	8.479%	$47.1992	$47.20	$47.20	$47.20
Purchase #6	$11.86	5.333%	$12.4925	$12.49	$12.50	$12.50
Purchase #7	$32.70	9.210%	$35.7117	$35.71	$35.70	$35.70
7 purchase totals =	$456.56		$500.5711	$500.56	$500.55	$500.60