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	$180.77	13.316%	$204.8413	$204.84	$204.85	$204.80
Purchase #2	$76.94	12.831%	$86.8122	$86.81	$86.80	$86.80
Purchase #3	$117.61	12.532%	$132.3489	$132.35	$132.35	$132.30
Purchase #4	$132.30	6.854%	$141.3678	$141.37	$141.35	$141.40
Purchase #5	$225.30	5.836%	$238.4485	$238.45	$238.45	$238.40
Purchase #6	$131.31	8.466%	$142.4267	$142.43	$142.45	$142.40
Purchase #7	$123.47	6.160%	$131.0758	$131.08	$131.10	$131.10
7 purchase totals =	$987.70		$1,077.3212	$1,077.33	$1,077.35	$1,077.20