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	$149.80	9.238%	$163.6385	$163.64	$163.65	$163.60
Purchase #2	$176.64	7.385%	$189.6849	$189.68	$189.70	$189.70
Purchase #3	$118.30	4.354%	$123.4508	$123.45	$123.45	$123.50
Purchase #4	$64.67	3.789%	$67.1203	$67.12	$67.10	$67.10
Purchase #5	$140.77	11.834%	$157.4287	$157.43	$157.45	$157.40
Purchase #6	$38.65	4.171%	$40.2621	$40.26	$40.25	$40.30
Purchase #7	$55.45	7.616%	$59.6731	$59.67	$59.65	$59.70
7 purchase totals =	$744.28		$801.2584	$801.25	$801.25	$801.30