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	$19.49	4.789%	$20.4234	$20.42	$20.40	$20.40
Purchase #2	$55.37	11.653%	$61.8223	$61.82	$61.80	$61.80
Purchase #3	$225.93	7.126%	$242.0298	$242.03	$242.05	$242.00
Purchase #4	$5.96	4.482%	$6.2271	$6.23	$6.25	$6.20
Purchase #5	$85.70	7.139%	$91.8181	$91.82	$91.80	$91.80
Purchase #6	$137.37	7.353%	$147.4708	$147.47	$147.45	$147.50
Purchase #7	$106.51	10.395%	$117.5817	$117.58	$117.60	$117.60
7 purchase totals =	$636.33		$687.3732	$687.37	$687.35	$687.30