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	$118.71	8.514%	$128.817	$128.82	$128.80	$128.80
Purchase #2	$40.52	6.451%	$43.1339	$43.13	$43.15	$43.10
Purchase #3	$68.47	13.681%	$77.8374	$77.84	$77.85	$77.80
Purchase #4	$233.94	13.782%	$266.1816	$266.18	$266.20	$266.20
Purchase #5	$226.43	10.150%	$249.4126	$249.41	$249.40	$249.40
Purchase #6	$171.58	9.872%	$188.5184	$188.52	$188.50	$188.50
Purchase #7	$6.60	11.839%	$7.3814	$7.38	$7.40	$7.40
7 purchase totals =	$866.25		$961.2823	$961.28	$961.30	$961.20