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	$102.47	7.814%	$110.477	$110.48	$110.50	$110.50
Purchase #2	$152.79	9.835%	$167.8169	$167.82	$167.80	$167.80
Purchase #3	$82.67	7.795%	$89.1141	$89.11	$89.10	$89.10
Purchase #4	$115.36	13.601%	$131.0501	$131.05	$131.05	$131.10
Purchase #5	$139.32	11.686%	$155.6009	$155.60	$155.60	$155.60
Purchase #6	$89.80	5.752%	$94.9653	$94.97	$94.95	$95.00
Purchase #7	$117.61	12.300%	$132.076	$132.08	$132.10	$132.10
7 purchase totals =	$800.02		$881.1003	$881.11	$881.10	$881.20