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	$17.92	8.534%	$19.4493	$19.45	$19.45	$19.40
Purchase #2	$236.25	12.864%	$266.6412	$266.64	$266.65	$266.60
Purchase #3	$37.30	8.870%	$40.6085	$40.61	$40.60	$40.60
Purchase #4	$101.26	4.439%	$105.7549	$105.75	$105.75	$105.80
Purchase #5	$55.48	7.567%	$59.6782	$59.68	$59.70	$59.70
Purchase #6	$147.37	3.116%	$151.962	$151.96	$151.95	$152.00
Purchase #7	$59.37	4.562%	$62.0785	$62.08	$62.10	$62.10
7 purchase totals =	$654.95		$706.1726	$706.17	$706.20	$706.20