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	$34.82	3.675%	$36.0996	$36.10	$36.10	$36.10
Purchase #2	$54.98	3.486%	$56.8966	$56.90	$56.90	$56.90
Purchase #3	$78.61	12.605%	$88.5188	$88.52	$88.50	$88.50
Purchase #4	$211.72	12.344%	$237.8547	$237.85	$237.85	$237.90
Purchase #5	$163.78	10.403%	$180.818	$180.82	$180.80	$180.80
Purchase #6	$147.52	4.341%	$153.9238	$153.92	$153.90	$153.90
Purchase #7	$121.94	8.590%	$132.4146	$132.41	$132.40	$132.40
7 purchase totals =	$813.37		$886.5261	$886.52	$886.45	$886.50