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	$21.37	10.278%	$23.5664	$23.57	$23.55	$23.60
Purchase #2	$72.78	10.735%	$80.5929	$80.59	$80.60	$80.60
Purchase #3	$64.79	4.258%	$67.5488	$67.55	$67.55	$67.50
Purchase #4	$35.97	9.872%	$39.521	$39.52	$39.50	$39.50
Purchase #5	$226.28	4.420%	$236.2816	$236.28	$236.30	$236.30
Purchase #6	$205.32	11.785%	$229.517	$229.52	$229.50	$229.50
Purchase #7	$111.97	10.401%	$123.616	$123.62	$123.60	$123.60
7 purchase totals =	$738.48		$800.6437	$800.65	$800.60	$800.60