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	$144.66	6.390%	$153.9038	$153.90	$153.90	$153.90
Purchase #2	$162.87	10.694%	$180.2873	$180.29	$180.30	$180.30
Purchase #3	$211.47	13.565%	$240.1559	$240.16	$240.15	$240.20
Purchase #4	$215.50	5.411%	$227.1607	$227.16	$227.15	$227.20
Purchase #5	$79.82	3.386%	$82.5227	$82.52	$82.50	$82.50
Purchase #6	$249.37	12.541%	$280.6435	$280.64	$280.65	$280.60
Purchase #7	$163.50	10.517%	$180.6953	$180.70	$180.70	$180.70
7 purchase totals =	$1,227.19		$1,345.3692	$1,345.37	$1,345.35	$1,345.40