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	$160.44	3.837%	$166.5961	$166.60	$166.60	$166.60
Purchase #2	$156.45	10.278%	$172.5299	$172.53	$172.55	$172.50
Purchase #3	$59.65	12.706%	$67.2291	$67.23	$67.25	$67.20
Purchase #4	$137.26	8.853%	$149.4116	$149.41	$149.40	$149.40
Purchase #5	$159.74	5.632%	$168.7366	$168.74	$168.75	$168.70
Purchase #6	$201.25	10.587%	$222.5563	$222.56	$222.55	$222.60
Purchase #7	$44.60	3.742%	$46.2689	$46.27	$46.25	$46.30
7 purchase totals =	$919.39		$993.3285	$993.34	$993.35	$993.30