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	$179.59	11.854%	$200.8786	$200.88	$200.90	$200.90
Purchase #2	$75.83	8.707%	$82.4325	$82.43	$82.45	$82.40
Purchase #3	$241.60	11.707%	$269.8841	$269.88	$269.90	$269.90
Purchase #4	$233.93	12.739%	$263.7303	$263.73	$263.75	$263.70
Purchase #5	$79.80	13.103%	$90.2562	$90.26	$90.25	$90.30
Purchase #6	$19.86	4.767%	$20.8067	$20.81	$20.80	$20.80
Purchase #7	$57.62	4.261%	$60.0752	$60.08	$60.10	$60.10
7 purchase totals =	$888.23		$988.0636	$988.07	$988.15	$988.10