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	$83.33	8.443%	$90.3656	$90.37	$90.35	$90.40
Purchase #2	$103.60	10.470%	$114.4469	$114.45	$114.45	$114.40
Purchase #3	$113.97	8.326%	$123.4591	$123.46	$123.45	$123.50
Purchase #4	$151.66	6.260%	$161.1539	$161.15	$161.15	$161.20
Purchase #5	$239.87	7.675%	$258.28	$258.28	$258.30	$258.30
Purchase #6	$64.93	6.467%	$69.129	$69.13	$69.15	$69.10
Purchase #7	$26.78	10.653%	$29.6329	$29.63	$29.65	$29.60
7 purchase totals =	$784.14		$846.4674	$846.47	$846.50	$846.50