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	$46.32	12.167%	$51.9558	$51.96	$51.95	$52.00
Purchase #2	$238.92	8.499%	$259.2258	$259.23	$259.25	$259.20
Purchase #3	$105.71	6.531%	$112.6139	$112.61	$112.60	$112.60
Purchase #4	$36.94	12.240%	$41.4615	$41.46	$41.45	$41.50
Purchase #5	$61.84	7.254%	$66.3259	$66.33	$66.35	$66.30
Purchase #6	$109.28	8.771%	$118.8649	$118.86	$118.85	$118.90
Purchase #7	$181.70	13.274%	$205.8189	$205.82	$205.80	$205.80
7 purchase totals =	$780.71		$856.2667	$856.27	$856.25	$856.30