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	$6.37	7.462%	$6.8453	$6.85	$6.85	$6.80
Purchase #2	$64.55	11.625%	$72.0539	$72.05	$72.05	$72.10
Purchase #3	$11.62	6.219%	$12.3426	$12.34	$12.35	$12.30
Purchase #4	$241.39	12.301%	$271.0834	$271.08	$271.10	$271.10
Purchase #5	$35.40	7.551%	$38.0731	$38.07	$38.05	$38.10
Purchase #6	$69.61	3.623%	$72.132	$72.13	$72.15	$72.10
Purchase #7	$44.43	10.340%	$49.0241	$49.02	$49.00	$49.00
7 purchase totals =	$473.37		$521.5544	$521.54	$521.55	$521.50