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	$10.90	11.565%	$12.1606	$12.16	$12.15	$12.20
Purchase #2	$6.55	4.630%	$6.8533	$6.85	$6.85	$6.90
Purchase #3	$155.46	6.601%	$165.7219	$165.72	$165.70	$165.70
Purchase #4	$40.77	8.599%	$44.2758	$44.28	$44.30	$44.30
Purchase #5	$155.59	4.414%	$162.4577	$162.46	$162.45	$162.50
Purchase #6	$92.84	4.658%	$97.1645	$97.16	$97.15	$97.20
Purchase #7	$59.34	10.296%	$65.4496	$65.45	$65.45	$65.40
7 purchase totals =	$521.45		$554.0834	$554.08	$554.05	$554.20