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	$166.47	11.500%	$185.6141	$185.61	$185.60	$185.60
Purchase #2	$132.79	6.709%	$141.6989	$141.70	$141.70	$141.70
Purchase #3	$40.77	4.303%	$42.5243	$42.52	$42.50	$42.50
Purchase #4	$230.90	3.410%	$238.7737	$238.77	$238.75	$238.80
Purchase #5	$95.34	7.132%	$102.1396	$102.14	$102.15	$102.10
Purchase #6	$53.88	3.249%	$55.6306	$55.63	$55.65	$55.60
Purchase #7	$56.95	6.372%	$60.5789	$60.58	$60.60	$60.60
7 purchase totals =	$777.10		$826.9601	$826.95	$826.95	$826.90