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	$11.26	8.235%	$12.1873	$12.19	$12.20	$12.20
Purchase #2	$38.56	11.504%	$42.9959	$43.00	$43.00	$43.00
Purchase #3	$80.36	6.257%	$85.3881	$85.39	$85.40	$85.40
Purchase #4	$74.61	10.260%	$82.265	$82.27	$82.25	$82.30
Purchase #5	$25.92	7.329%	$27.8197	$27.82	$27.80	$27.80
Purchase #6	$153.33	13.585%	$174.1599	$174.16	$174.15	$174.20
Purchase #7	$195.67	9.640%	$214.5326	$214.53	$214.55	$214.50
7 purchase totals =	$579.71		$639.3485	$639.36	$639.35	$639.40