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	$205.58	5.159%	$216.1859	$216.19	$216.20	$216.20
Purchase #2	$198.38	10.151%	$218.5176	$218.52	$218.50	$218.50
Purchase #3	$90.38	6.867%	$96.5864	$96.59	$96.60	$96.60
Purchase #4	$40.55	5.162%	$42.6432	$42.64	$42.65	$42.60
Purchase #5	$154.86	13.339%	$175.5168	$175.52	$175.50	$175.50
Purchase #6	$53.65	13.381%	$60.8289	$60.83	$60.85	$60.80
Purchase #7	$86.95	10.374%	$95.9702	$95.97	$95.95	$96.00
7 purchase totals =	$830.35		$906.2490	$906.26	$906.25	$906.20