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	$17.89	5.218%	$18.8235	$18.82	$18.80	$18.80
Purchase #2	$65.68	5.297%	$69.1591	$69.16	$69.15	$69.20
Purchase #3	$109.81	11.691%	$122.6479	$122.65	$122.65	$122.60
Purchase #4	$67.81	5.726%	$71.6928	$71.69	$71.70	$71.70
Purchase #5	$54.79	13.866%	$62.3872	$62.39	$62.40	$62.40
Purchase #6	$28.94	10.684%	$32.0319	$32.03	$32.05	$32.00
Purchase #7	$50.30	4.530%	$52.5786	$52.58	$52.60	$52.60
7 purchase totals =	$395.22		$429.3210	$429.32	$429.35	$429.30