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	$228.72	4.468%	$238.9392	$238.94	$238.95	$238.90
Purchase #2	$140.66	6.724%	$150.118	$150.12	$150.10	$150.10
Purchase #3	$61.62	7.138%	$66.0184	$66.02	$66.00	$66.00
Purchase #4	$105.77	6.642%	$112.7952	$112.80	$112.80	$112.80
Purchase #5	$101.70	10.493%	$112.3714	$112.37	$112.35	$112.40
Purchase #6	$89.82	11.745%	$100.3694	$100.37	$100.35	$100.40
Purchase #7	$152.26	9.339%	$166.4796	$166.48	$166.50	$166.50
7 purchase totals =	$880.55		$947.0912	$947.10	$947.05	$947.10