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	$26.97	7.334%	$28.948	$28.95	$28.95	$28.90
Purchase #2	$124.28	10.246%	$137.0137	$137.01	$137.00	$137.00
Purchase #3	$56.67	13.528%	$64.3363	$64.34	$64.35	$64.30
Purchase #4	$134.28	9.745%	$147.3656	$147.37	$147.35	$147.40
Purchase #5	$91.43	9.636%	$100.2402	$100.24	$100.25	$100.20
Purchase #6	$120.87	5.729%	$127.7946	$127.79	$127.80	$127.80
Purchase #7	$90.95	13.518%	$103.2446	$103.24	$103.25	$103.20
7 purchase totals =	$645.45		$708.9430	$708.94	$708.95	$708.80