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	$90.73	9.616%	$99.4546	$99.45	$99.45	$99.50
Purchase #2	$27.83	13.632%	$31.6238	$31.62	$31.60	$31.60
Purchase #3	$204.73	11.201%	$227.6618	$227.66	$227.65	$227.70
Purchase #4	$98.31	5.292%	$103.5126	$103.51	$103.50	$103.50
Purchase #5	$161.67	10.163%	$178.1005	$178.10	$178.10	$178.10
Purchase #6	$100.64	5.608%	$106.2839	$106.28	$106.30	$106.30
Purchase #7	$49.33	6.363%	$52.4689	$52.47	$52.45	$52.50
7 purchase totals =	$733.24		$799.1061	$799.09	$799.05	$799.20