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	$30.52	12.746%	$34.4101	$34.41	$34.40	$34.40
Purchase #2	$189.75	10.403%	$209.4897	$209.49	$209.50	$209.50
Purchase #3	$69.60	12.810%	$78.5158	$78.52	$78.50	$78.50
Purchase #4	$80.32	11.165%	$89.2877	$89.29	$89.30	$89.30
Purchase #5	$132.69	3.317%	$137.0913	$137.09	$137.10	$137.10
Purchase #6	$175.83	11.342%	$195.7726	$195.77	$195.75	$195.80
Purchase #7	$142.34	11.420%	$158.5952	$158.60	$158.60	$158.60
7 purchase totals =	$821.05		$903.1624	$903.17	$903.15	$903.20