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	$99.60	11.745%	$111.298	$111.30	$111.30	$111.30
Purchase #2	$115.81	10.540%	$128.0164	$128.02	$128.00	$128.00
Purchase #3	$131.62	10.357%	$145.2519	$145.25	$145.25	$145.30
Purchase #4	$77.69	8.353%	$84.1794	$84.18	$84.20	$84.20
Purchase #5	$5.41	5.502%	$5.7077	$5.71	$5.70	$5.70
Purchase #6	$156.29	7.801%	$168.4822	$168.48	$168.50	$168.50
Purchase #7	$105.93	5.559%	$111.8186	$111.82	$111.80	$111.80
7 purchase totals =	$692.35		$754.7542	$754.76	$754.75	$754.80