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	$202.70	6.728%	$216.3377	$216.34	$216.35	$216.30
Purchase #2	$96.88	8.504%	$105.1187	$105.12	$105.10	$105.10
Purchase #3	$39.35	10.552%	$43.5022	$43.50	$43.50	$43.50
Purchase #4	$129.85	7.432%	$139.5005	$139.50	$139.50	$139.50
Purchase #5	$25.27	7.761%	$27.2312	$27.23	$27.25	$27.20
Purchase #6	$15.87	10.849%	$17.5917	$17.59	$17.60	$17.60
Purchase #7	$51.25	13.720%	$58.2815	$58.28	$58.30	$58.30
7 purchase totals =	$561.17		$607.5635	$607.56	$607.60	$607.50