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	$21.56	9.570%	$23.6233	$23.62	$23.60	$23.60
Purchase #2	$56.86	8.540%	$61.7158	$61.72	$61.70	$61.70
Purchase #3	$111.75	10.353%	$123.3195	$123.32	$123.30	$123.30
Purchase #4	$180.88	12.280%	$203.0921	$203.09	$203.10	$203.10
Purchase #5	$186.67	3.335%	$192.8954	$192.90	$192.90	$192.90
Purchase #6	$240.66	13.345%	$272.7761	$272.78	$272.80	$272.80
Purchase #7	$53.53	10.548%	$59.1763	$59.18	$59.20	$59.20
7 purchase totals =	$851.91		$936.5985	$936.61	$936.60	$936.60