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	$236.91	11.176%	$263.3871	$263.39	$263.40	$263.40
Purchase #2	$42.25	7.395%	$45.3744	$45.37	$45.35	$45.40
Purchase #3	$121.86	9.407%	$133.3234	$133.32	$133.30	$133.30
Purchase #4	$233.30	9.829%	$256.2311	$256.23	$256.25	$256.20
Purchase #5	$98.97	12.694%	$111.5333	$111.53	$111.55	$111.50
Purchase #6	$45.41	13.580%	$51.5767	$51.58	$51.60	$51.60
Purchase #7	$215.50	12.134%	$241.6488	$241.65	$241.65	$241.60
7 purchase totals =	$994.20		$1,103.0748	$1,103.07	$1,103.10	$1,103.00