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	$239.57	4.559%	$250.492	$250.49	$250.50	$250.50
Purchase #2	$92.96	9.615%	$101.8981	$101.90	$101.90	$101.90
Purchase #3	$73.52	11.825%	$82.2137	$82.21	$82.20	$82.20
Purchase #4	$132.35	6.379%	$140.7926	$140.79	$140.80	$140.80
Purchase #5	$134.83	12.282%	$151.3898	$151.39	$151.40	$151.40
Purchase #6	$155.67	13.616%	$176.866	$176.87	$176.85	$176.90
Purchase #7	$230.42	13.635%	$261.8378	$261.84	$261.85	$261.80
7 purchase totals =	$1,059.32		$1,165.4900	$1,165.49	$1,165.50	$1,165.50