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	$239.30	10.861%	$265.2904	$265.29	$265.30	$265.30
Purchase #2	$27.44	6.197%	$29.1405	$29.14	$29.15	$29.10
Purchase #3	$68.32	3.620%	$70.7932	$70.79	$70.80	$70.80
Purchase #4	$48.52	11.828%	$54.2589	$54.26	$54.25	$54.30
Purchase #5	$26.63	3.130%	$27.4635	$27.46	$27.45	$27.50
Purchase #6	$150.35	3.748%	$155.9851	$155.99	$156.00	$156.00
Purchase #7	$81.51	11.524%	$90.9032	$90.90	$90.90	$90.90
7 purchase totals =	$642.07		$693.8348	$693.83	$693.85	$693.90