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	$59.56	11.122%	$66.1843	$66.18	$66.20	$66.20
Purchase #2	$139.54	9.283%	$152.4935	$152.49	$152.50	$152.50
Purchase #3	$84.62	3.532%	$87.6088	$87.61	$87.60	$87.60
Purchase #4	$222.80	6.865%	$238.0952	$238.10	$238.10	$238.10
Purchase #5	$79.61	12.488%	$89.5517	$89.55	$89.55	$89.60
Purchase #6	$99.86	12.765%	$112.6071	$112.61	$112.60	$112.60
Purchase #7	$45.62	9.553%	$49.9781	$49.98	$50.00	$50.00
7 purchase totals =	$731.61		$796.5187	$796.52	$796.55	$796.60