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	$146.35	9.586%	$160.3791	$160.38	$160.40	$160.40
Purchase #2	$218.69	5.647%	$231.0394	$231.04	$231.05	$231.00
Purchase #3	$105.71	10.571%	$116.8846	$116.88	$116.90	$116.90
Purchase #4	$8.98	5.370%	$9.4622	$9.46	$9.45	$9.50
Purchase #5	$94.43	7.220%	$101.2478	$101.25	$101.25	$101.20
Purchase #6	$87.83	3.287%	$90.717	$90.72	$90.70	$90.70
Purchase #7	$65.81	7.298%	$70.6128	$70.61	$70.60	$70.60
7 purchase totals =	$727.80		$780.3429	$780.34	$780.35	$780.30