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	$20.40	6.782%	$21.7835	$21.78	$21.80	$21.80
Purchase #2	$45.82	13.853%	$52.1674	$52.17	$52.15	$52.20
Purchase #3	$29.43	10.828%	$32.6167	$32.62	$32.60	$32.60
Purchase #4	$89.56	3.177%	$92.4053	$92.41	$92.40	$92.40
Purchase #5	$79.49	3.856%	$82.5551	$82.56	$82.55	$82.60
Purchase #6	$197.54	7.388%	$212.1343	$212.13	$212.15	$212.10
Purchase #7	$48.67	7.601%	$52.3694	$52.37	$52.35	$52.40
7 purchase totals =	$510.91		$546.0317	$546.04	$546.00	$546.10