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	$249.82	13.342%	$283.151	$283.15	$283.15	$283.20
Purchase #2	$194.83	4.139%	$202.894	$202.89	$202.90	$202.90
Purchase #3	$19.90	6.782%	$21.2496	$21.25	$21.25	$21.20
Purchase #4	$43.44	4.181%	$45.2562	$45.26	$45.25	$45.30
Purchase #5	$18.60	9.858%	$20.4336	$20.43	$20.45	$20.40
Purchase #6	$131.34	4.295%	$136.9811	$136.98	$137.00	$137.00
Purchase #7	$125.50	9.577%	$137.5191	$137.52	$137.50	$137.50
7 purchase totals =	$783.43		$847.4846	$847.48	$847.50	$847.50