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	$121.43	7.267%	$130.2543	$130.25	$130.25	$130.30
Purchase #2	$96.83	13.384%	$109.7897	$109.79	$109.80	$109.80
Purchase #3	$86.84	11.661%	$96.9664	$96.97	$96.95	$97.00
Purchase #4	$40.94	10.458%	$45.2215	$45.22	$45.20	$45.20
Purchase #5	$51.60	10.191%	$56.8586	$56.86	$56.85	$56.90
Purchase #6	$83.47	3.211%	$86.1502	$86.15	$86.15	$86.20
Purchase #7	$48.56	7.578%	$52.2399	$52.24	$52.25	$52.20
7 purchase totals =	$529.67		$577.4806	$577.48	$577.45	$577.60