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	$34.37	11.202%	$38.2201	$38.22	$38.20	$38.20
Purchase #2	$193.55	4.825%	$202.8888	$202.89	$202.90	$202.90
Purchase #3	$21.38	11.327%	$23.8017	$23.80	$23.80	$23.80
Purchase #4	$76.60	7.830%	$82.5978	$82.60	$82.60	$82.60
Purchase #5	$143.89	4.469%	$150.3204	$150.32	$150.30	$150.30
Purchase #6	$52.79	12.775%	$59.5339	$59.53	$59.55	$59.50
Purchase #7	$128.27	10.698%	$141.9923	$141.99	$142.00	$142.00
7 purchase totals =	$650.85		$699.3550	$699.35	$699.35	$699.30