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	$146.54	12.171%	$164.3754	$164.38	$164.40	$164.40
Purchase #2	$117.77	13.846%	$134.0764	$134.08	$134.10	$134.10
Purchase #3	$243.65	4.566%	$254.7751	$254.78	$254.80	$254.80
Purchase #4	$78.89	5.455%	$83.1934	$83.19	$83.20	$83.20
Purchase #5	$128.57	7.690%	$138.457	$138.46	$138.45	$138.50
Purchase #6	$103.39	7.516%	$111.1608	$111.16	$111.15	$111.20
Purchase #7	$44.85	5.869%	$47.4822	$47.48	$47.50	$47.50
7 purchase totals =	$863.66		$933.5203	$933.53	$933.60	$933.70