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	$21.43	13.359%	$24.2928	$24.29	$24.30	$24.30
Purchase #2	$148.73	9.312%	$162.5797	$162.58	$162.60	$162.60
Purchase #3	$178.27	5.870%	$188.7344	$188.73	$188.75	$188.70
Purchase #4	$141.39	6.466%	$150.5323	$150.53	$150.55	$150.50
Purchase #5	$144.86	8.317%	$156.908	$156.91	$156.90	$156.90
Purchase #6	$40.42	11.643%	$45.1261	$45.13	$45.15	$45.10
Purchase #7	$87.69	4.407%	$91.5545	$91.55	$91.55	$91.60
7 purchase totals =	$762.79		$819.7278	$819.72	$819.80	$819.70