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	$50.46	12.706%	$56.8714	$56.87	$56.85	$56.90
Purchase #2	$38.29	4.556%	$40.0345	$40.03	$40.05	$40.00
Purchase #3	$160.81	7.521%	$172.9045	$172.90	$172.90	$172.90
Purchase #4	$90.92	8.621%	$98.7582	$98.76	$98.75	$98.80
Purchase #5	$103.30	8.476%	$112.0557	$112.06	$112.05	$112.10
Purchase #6	$26.88	3.175%	$27.7334	$27.73	$27.75	$27.70
Purchase #7	$168.52	3.522%	$174.4553	$174.46	$174.45	$174.50
7 purchase totals =	$639.18		$682.8130	$682.81	$682.80	$682.90