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	$126.46	7.645%	$136.1279	$136.13	$136.15	$136.10
Purchase #2	$57.56	3.377%	$59.5038	$59.50	$59.50	$59.50
Purchase #3	$184.68	10.690%	$204.4223	$204.42	$204.40	$204.40
Purchase #4	$212.61	13.301%	$240.8893	$240.89	$240.90	$240.90
Purchase #5	$218.52	5.793%	$231.1789	$231.18	$231.20	$231.20
Purchase #6	$142.92	5.154%	$150.2861	$150.29	$150.30	$150.30
Purchase #7	$241.29	4.800%	$252.8719	$252.87	$252.85	$252.90
7 purchase totals =	$1,184.04		$1,275.2802	$1,275.28	$1,275.30	$1,275.30