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	$205.97	7.518%	$221.4548	$221.45	$221.45	$221.50
Purchase #2	$40.74	12.584%	$45.8667	$45.87	$45.85	$45.90
Purchase #3	$53.38	5.466%	$56.2978	$56.30	$56.30	$56.30
Purchase #4	$74.79	12.172%	$83.8934	$83.89	$83.90	$83.90
Purchase #5	$48.86	10.375%	$53.9292	$53.93	$53.95	$53.90
Purchase #6	$132.43	6.479%	$141.0101	$141.01	$141.00	$141.00
Purchase #7	$89.40	9.694%	$98.0664	$98.07	$98.05	$98.10
7 purchase totals =	$645.57		$700.5184	$700.52	$700.50	$700.60