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	$205.72	6.648%	$219.3963	$219.40	$219.40	$219.40
Purchase #2	$30.58	7.558%	$32.8912	$32.89	$32.90	$32.90
Purchase #3	$9.63	8.698%	$10.4676	$10.47	$10.45	$10.50
Purchase #4	$162.82	5.483%	$171.7474	$171.75	$171.75	$171.70
Purchase #5	$108.49	4.622%	$113.5044	$113.50	$113.50	$113.50
Purchase #6	$157.56	4.126%	$164.0609	$164.06	$164.05	$164.10
Purchase #7	$131.70	7.692%	$141.8304	$141.83	$141.85	$141.80
7 purchase totals =	$806.50		$853.8982	$853.90	$853.90	$853.90