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	$18.94	7.395%	$20.3406	$20.34	$20.35	$20.30
Purchase #2	$114.44	11.627%	$127.7459	$127.75	$127.75	$127.70
Purchase #3	$21.28	11.470%	$23.7208	$23.72	$23.70	$23.70
Purchase #4	$98.85	3.289%	$102.1012	$102.10	$102.10	$102.10
Purchase #5	$82.26	11.379%	$91.6204	$91.62	$91.60	$91.60
Purchase #6	$208.69	4.856%	$218.824	$218.82	$218.80	$218.80
Purchase #7	$94.85	12.294%	$106.5109	$106.51	$106.50	$106.50
7 purchase totals =	$639.31		$690.8638	$690.86	$690.80	$690.70