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	$138.50	13.746%	$157.5382	$157.54	$157.55	$157.50
Purchase #2	$164.46	13.838%	$187.218	$187.22	$187.20	$187.20
Purchase #3	$85.42	5.451%	$90.0762	$90.08	$90.10	$90.10
Purchase #4	$229.67	5.735%	$242.8416	$242.84	$242.85	$242.80
Purchase #5	$99.43	11.169%	$110.5353	$110.54	$110.55	$110.50
Purchase #6	$38.71	11.653%	$43.2209	$43.22	$43.20	$43.20
Purchase #7	$66.26	8.742%	$72.0524	$72.05	$72.05	$72.10
7 purchase totals =	$822.45		$903.4826	$903.49	$903.50	$903.40