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	$17.37	5.764%	$18.3712	$18.37	$18.35	$18.40
Purchase #2	$184.27	11.645%	$205.7282	$205.73	$205.75	$205.70
Purchase #3	$16.32	5.156%	$17.1615	$17.16	$17.15	$17.20
Purchase #4	$86.31	9.198%	$94.2488	$94.25	$94.25	$94.20
Purchase #5	$166.42	11.519%	$185.5899	$185.59	$185.60	$185.60
Purchase #6	$104.73	6.298%	$111.3259	$111.33	$111.35	$111.30
Purchase #7	$221.27	5.849%	$234.2121	$234.21	$234.20	$234.20
7 purchase totals =	$796.69		$866.6376	$866.64	$866.65	$866.60