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	$56.83	6.719%	$60.6484	$60.65	$60.65	$60.60
Purchase #2	$182.54	4.423%	$190.6137	$190.61	$190.60	$190.60
Purchase #3	$208.76	7.281%	$223.9598	$223.96	$223.95	$224.00
Purchase #4	$119.36	12.634%	$134.4399	$134.44	$134.45	$134.40
Purchase #5	$150.49	5.223%	$158.3501	$158.35	$158.35	$158.40
Purchase #6	$193.50	11.699%	$216.1376	$216.14	$216.15	$216.10
Purchase #7	$93.79	12.400%	$105.42	$105.42	$105.40	$105.40
7 purchase totals =	$1,005.27		$1,089.5695	$1,089.57	$1,089.55	$1,089.50