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	$62.88	5.579%	$66.3881	$66.39	$66.40	$66.40
Purchase #2	$81.31	3.643%	$84.2721	$84.27	$84.25	$84.30
Purchase #3	$32.53	7.765%	$35.056	$35.06	$35.05	$35.10
Purchase #4	$79.78	3.488%	$82.5627	$82.56	$82.55	$82.60
Purchase #5	$218.96	6.484%	$233.1574	$233.16	$233.15	$233.20
Purchase #6	$38.35	13.672%	$43.5932	$43.59	$43.60	$43.60
Purchase #7	$85.28	10.620%	$94.3367	$94.34	$94.35	$94.30
7 purchase totals =	$599.09		$639.3662	$639.37	$639.35	$639.50