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	$183.80	8.474%	$199.3752	$199.38	$199.40	$199.40
Purchase #2	$112.80	9.333%	$123.3276	$123.33	$123.35	$123.30
Purchase #3	$85.83	6.105%	$91.0699	$91.07	$91.05	$91.10
Purchase #4	$78.88	13.190%	$89.2843	$89.28	$89.30	$89.30
Purchase #5	$117.92	11.241%	$131.1754	$131.18	$131.20	$131.20
Purchase #6	$210.50	10.804%	$233.2424	$233.24	$233.25	$233.20
Purchase #7	$118.84	7.257%	$127.4642	$127.46	$127.45	$127.50
7 purchase totals =	$908.57		$994.9390	$994.94	$995.00	$995.00