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	$71.88	11.431%	$80.0966	$80.10	$80.10	$80.10
Purchase #2	$79.70	3.372%	$82.3875	$82.39	$82.40	$82.40
Purchase #3	$46.87	3.512%	$48.5161	$48.52	$48.50	$48.50
Purchase #4	$83.35	9.156%	$90.9815	$90.98	$91.00	$91.00
Purchase #5	$93.66	10.576%	$103.5655	$103.57	$103.55	$103.60
Purchase #6	$20.60	4.777%	$21.5841	$21.58	$21.60	$21.60
Purchase #7	$64.85	12.652%	$73.0548	$73.05	$73.05	$73.10
7 purchase totals =	$460.91		$500.1861	$500.19	$500.20	$500.30