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	$80.96	11.828%	$90.5359	$90.54	$90.55	$90.50
Purchase #2	$114.76	7.670%	$123.5621	$123.56	$123.55	$123.60
Purchase #3	$100.49	12.245%	$112.795	$112.80	$112.80	$112.80
Purchase #4	$148.25	12.351%	$166.5604	$166.56	$166.55	$166.60
Purchase #5	$146.37	4.297%	$152.6595	$152.66	$152.65	$152.70
Purchase #6	$191.42	13.175%	$216.6396	$216.64	$216.65	$216.60
Purchase #7	$118.40	8.597%	$128.5788	$128.58	$128.60	$128.60
7 purchase totals =	$900.65		$991.3313	$991.34	$991.35	$991.40