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	$79.57	13.859%	$90.5976	$90.60	$90.60	$90.60
Purchase #2	$125.69	11.635%	$140.314	$140.31	$140.30	$140.30
Purchase #3	$132.25	13.476%	$150.072	$150.07	$150.05	$150.10
Purchase #4	$94.47	13.499%	$107.2225	$107.22	$107.20	$107.20
Purchase #5	$203.50	13.298%	$230.5614	$230.56	$230.55	$230.60
Purchase #6	$205.63	6.201%	$218.3811	$218.38	$218.40	$218.40
Purchase #7	$115.94	12.746%	$130.7177	$130.72	$130.70	$130.70
7 purchase totals =	$957.05		$1,067.8663	$1,067.86	$1,067.80	$1,067.90