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	$158.67	12.636%	$178.7195	$178.72	$178.70	$178.70
Purchase #2	$109.55	6.697%	$116.8866	$116.89	$116.90	$116.90
Purchase #3	$35.32	8.525%	$38.331	$38.33	$38.35	$38.30
Purchase #4	$142.86	6.358%	$151.943	$151.94	$151.95	$151.90
Purchase #5	$73.57	5.855%	$77.8775	$77.88	$77.90	$77.90
Purchase #6	$124.48	8.363%	$134.8903	$134.89	$134.90	$134.90
Purchase #7	$5.95	13.588%	$6.7585	$6.76	$6.75	$6.80
7 purchase totals =	$650.40		$705.4064	$705.41	$705.45	$705.40