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	$171.45	6.510%	$182.6114	$182.61	$182.60	$182.60
Purchase #2	$37.98	13.482%	$43.1005	$43.10	$43.10	$43.10
Purchase #3	$53.76	13.546%	$61.0423	$61.04	$61.05	$61.00
Purchase #4	$95.40	13.693%	$108.4631	$108.46	$108.45	$108.50
Purchase #5	$33.50	9.573%	$36.707	$36.71	$36.70	$36.70
Purchase #6	$78.67	3.482%	$81.4093	$81.41	$81.40	$81.40
Purchase #7	$60.63	9.382%	$66.3183	$66.32	$66.30	$66.30
7 purchase totals =	$531.39		$579.6519	$579.65	$579.60	$579.60