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	$247.28	13.574%	$280.8458	$280.85	$280.85	$280.80
Purchase #2	$131.71	11.283%	$146.5708	$146.57	$146.55	$146.60
Purchase #3	$167.65	8.624%	$182.1081	$182.11	$182.10	$182.10
Purchase #4	$15.68	13.722%	$17.8316	$17.83	$17.85	$17.80
Purchase #5	$31.46	3.148%	$32.4504	$32.45	$32.45	$32.50
Purchase #6	$52.79	11.325%	$58.7685	$58.77	$58.75	$58.80
Purchase #7	$65.51	10.296%	$72.2549	$72.25	$72.25	$72.30
7 purchase totals =	$712.08		$790.8301	$790.83	$790.80	$790.90