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	$38.58	8.713%	$41.9415	$41.94	$41.95	$41.90
Purchase #2	$35.31	13.382%	$40.0352	$40.04	$40.05	$40.00
Purchase #3	$215.80	13.670%	$245.2999	$245.30	$245.30	$245.30
Purchase #4	$28.95	7.162%	$31.0234	$31.02	$31.00	$31.00
Purchase #5	$35.82	12.303%	$40.2269	$40.23	$40.25	$40.20
Purchase #6	$43.83	12.157%	$49.1584	$49.16	$49.15	$49.20
Purchase #7	$51.38	11.351%	$57.2121	$57.21	$57.20	$57.20
7 purchase totals =	$449.67		$504.8974	$504.90	$504.90	$504.80