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	$96.48	3.268%	$99.633	$99.63	$99.65	$99.60
Purchase #2	$177.67	4.536%	$185.7291	$185.73	$185.75	$185.70
Purchase #3	$113.81	8.748%	$123.7661	$123.77	$123.75	$123.80
Purchase #4	$89.25	11.684%	$99.678	$99.68	$99.70	$99.70
Purchase #5	$160.82	13.434%	$182.4246	$182.42	$182.40	$182.40
Purchase #6	$190.95	12.498%	$214.8149	$214.81	$214.80	$214.80
Purchase #7	$44.51	13.498%	$50.518	$50.52	$50.50	$50.50
7 purchase totals =	$873.49		$956.5637	$956.56	$956.55	$956.50