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	$80.36	4.106%	$83.6596	$83.66	$83.65	$83.70
Purchase #2	$101.95	7.117%	$109.2058	$109.21	$109.20	$109.20
Purchase #3	$98.42	5.802%	$104.1303	$104.13	$104.15	$104.10
Purchase #4	$38.95	8.758%	$42.3612	$42.36	$42.35	$42.40
Purchase #5	$240.51	9.556%	$263.4931	$263.49	$263.50	$263.50
Purchase #6	$16.97	3.189%	$17.5112	$17.51	$17.50	$17.50
Purchase #7	$106.56	5.594%	$112.521	$112.52	$112.50	$112.50
7 purchase totals =	$683.72		$732.8822	$732.88	$732.85	$732.90