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	$204.90	4.665%	$214.4586	$214.46	$214.45	$214.50
Purchase #2	$192.87	6.171%	$204.772	$204.77	$204.75	$204.80
Purchase #3	$158.81	8.139%	$171.7355	$171.74	$171.75	$171.70
Purchase #4	$81.85	11.690%	$91.4183	$91.42	$91.40	$91.40
Purchase #5	$119.54	8.624%	$129.8491	$129.85	$129.85	$129.80
Purchase #6	$52.41	5.190%	$55.1301	$55.13	$55.15	$55.10
Purchase #7	$100.94	10.409%	$111.4468	$111.45	$111.45	$111.40
7 purchase totals =	$911.32		$978.8104	$978.82	$978.80	$978.70