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	$6.96	11.113%	$7.7335	$7.73	$7.75	$7.70
Purchase #2	$157.55	5.377%	$166.0215	$166.02	$166.00	$166.00
Purchase #3	$66.82	8.779%	$72.6861	$72.69	$72.70	$72.70
Purchase #4	$177.94	10.479%	$196.5863	$196.59	$196.60	$196.60
Purchase #5	$7.50	3.543%	$7.7657	$7.77	$7.75	$7.80
Purchase #6	$66.51	12.532%	$74.845	$74.85	$74.85	$74.80
Purchase #7	$69.89	10.791%	$77.4318	$77.43	$77.45	$77.40
7 purchase totals =	$553.17		$603.0699	$603.08	$603.10	$603.00