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	$102.34	9.262%	$111.8187	$111.82	$111.80	$111.80
Purchase #2	$99.37	9.844%	$109.152	$109.15	$109.15	$109.20
Purchase #3	$20.74	8.109%	$22.4218	$22.42	$22.40	$22.40
Purchase #4	$123.49	8.681%	$134.2102	$134.21	$134.20	$134.20
Purchase #5	$39.83	8.275%	$43.1259	$43.13	$43.15	$43.10
Purchase #6	$58.65	13.465%	$66.5472	$66.55	$66.55	$66.50
Purchase #7	$51.36	6.654%	$54.7775	$54.78	$54.80	$54.80
7 purchase totals =	$495.78		$542.0533	$542.06	$542.05	$542.00