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	$218.28	5.807%	$230.9555	$230.96	$230.95	$231.00
Purchase #2	$82.36	10.286%	$90.8315	$90.83	$90.85	$90.80
Purchase #3	$162.65	6.178%	$172.6985	$172.70	$172.70	$172.70
Purchase #4	$35.44	10.595%	$39.1949	$39.19	$39.20	$39.20
Purchase #5	$10.76	11.659%	$12.0145	$12.01	$12.00	$12.00
Purchase #6	$78.63	8.147%	$85.036	$85.04	$85.05	$85.00
Purchase #7	$80.76	12.478%	$90.8372	$90.84	$90.85	$90.80
7 purchase totals =	$668.88		$721.5681	$721.57	$721.60	$721.50