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	$54.26	7.217%	$58.1759	$58.18	$58.20	$58.20
Purchase #2	$173.57	3.780%	$180.1309	$180.13	$180.15	$180.10
Purchase #3	$250.79	11.723%	$280.1901	$280.19	$280.20	$280.20
Purchase #4	$157.28	13.266%	$178.1448	$178.14	$178.15	$178.10
Purchase #5	$239.83	8.235%	$259.58	$259.58	$259.60	$259.60
Purchase #6	$18.39	4.848%	$19.2815	$19.28	$19.30	$19.30
Purchase #7	$104.60	6.495%	$111.3938	$111.39	$111.40	$111.40
7 purchase totals =	$998.72		$1,086.8970	$1,086.89	$1,087.00	$1,086.90