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	$27.54	8.594%	$29.9068	$29.91	$29.90	$29.90
Purchase #2	$181.77	3.215%	$187.6139	$187.61	$187.60	$187.60
Purchase #3	$190.48	4.244%	$198.564	$198.56	$198.55	$198.60
Purchase #4	$89.42	11.675%	$99.8598	$99.86	$99.85	$99.90
Purchase #5	$248.75	10.866%	$275.7792	$275.78	$275.80	$275.80
Purchase #6	$243.81	9.599%	$267.2133	$267.21	$267.20	$267.20
Purchase #7	$87.50	8.360%	$94.815	$94.82	$94.80	$94.80
7 purchase totals =	$1,069.27		$1,153.7520	$1,153.75	$1,153.70	$1,153.80