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	$34.96	5.486%	$36.8779	$36.88	$36.90	$36.90
Purchase #2	$42.38	13.848%	$48.2488	$48.25	$48.25	$48.20
Purchase #3	$249.46	8.821%	$271.4649	$271.46	$271.45	$271.50
Purchase #4	$60.42	13.598%	$68.6359	$68.64	$68.65	$68.60
Purchase #5	$80.51	12.409%	$90.5005	$90.50	$90.50	$90.50
Purchase #6	$20.50	6.130%	$21.7567	$21.76	$21.75	$21.80
Purchase #7	$158.80	13.560%	$180.3333	$180.33	$180.35	$180.30
7 purchase totals =	$647.03		$717.8180	$717.82	$717.85	$717.80