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	$142.90	9.568%	$156.5727	$156.57	$156.55	$156.60
Purchase #2	$91.36	12.136%	$102.4474	$102.45	$102.45	$102.40
Purchase #3	$36.75	7.281%	$39.4258	$39.43	$39.45	$39.40
Purchase #4	$101.54	10.665%	$112.3692	$112.37	$112.35	$112.40
Purchase #5	$82.88	9.320%	$90.6044	$90.60	$90.60	$90.60
Purchase #6	$154.59	12.329%	$173.6494	$173.65	$173.65	$173.60
Purchase #7	$118.86	11.745%	$132.8201	$132.82	$132.80	$132.80
7 purchase totals =	$728.88		$807.8890	$807.89	$807.85	$807.80