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	$25.37	11.330%	$28.2444	$28.24	$28.25	$28.20
Purchase #2	$101.53	7.466%	$109.1102	$109.11	$109.10	$109.10
Purchase #3	$20.50	6.152%	$21.7612	$21.76	$21.75	$21.80
Purchase #4	$45.90	6.852%	$49.0451	$49.05	$49.05	$49.00
Purchase #5	$99.36	4.278%	$103.6106	$103.61	$103.60	$103.60
Purchase #6	$185.85	7.864%	$200.4652	$200.47	$200.45	$200.50
Purchase #7	$226.49	11.670%	$252.9214	$252.92	$252.90	$252.90
7 purchase totals =	$705.00		$765.1581	$765.16	$765.10	$765.10