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	$15.90	4.740%	$16.6537	$16.65	$16.65	$16.70
Purchase #2	$38.72	3.418%	$40.0434	$40.04	$40.05	$40.00
Purchase #3	$207.55	12.520%	$233.5353	$233.54	$233.55	$233.50
Purchase #4	$229.29	8.546%	$248.8851	$248.89	$248.90	$248.90
Purchase #5	$56.83	5.280%	$59.8306	$59.83	$59.85	$59.80
Purchase #6	$211.75	10.860%	$234.7461	$234.75	$234.75	$234.70
Purchase #7	$157.51	10.378%	$173.8564	$173.86	$173.85	$173.90
7 purchase totals =	$917.55		$1,007.5506	$1,007.56	$1,007.60	$1,007.50