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	$35.30	9.128%	$38.5222	$38.52	$38.50	$38.50
Purchase #2	$172.78	3.308%	$178.4956	$178.50	$178.50	$178.50
Purchase #3	$178.89	13.376%	$202.8183	$202.82	$202.80	$202.80
Purchase #4	$185.65	9.389%	$203.0807	$203.08	$203.10	$203.10
Purchase #5	$16.52	10.529%	$18.2594	$18.26	$18.25	$18.30
Purchase #6	$109.89	9.595%	$120.4339	$120.43	$120.45	$120.40
Purchase #7	$196.82	13.204%	$222.8081	$222.81	$222.80	$222.80
7 purchase totals =	$895.85		$984.4182	$984.42	$984.40	$984.40