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	$247.63	6.211%	$263.0103	$263.01	$263.00	$263.00
Purchase #2	$40.83	13.573%	$46.3719	$46.37	$46.35	$46.40
Purchase #3	$224.82	7.215%	$241.0408	$241.04	$241.05	$241.00
Purchase #4	$113.38	7.184%	$121.5252	$121.53	$121.55	$121.50
Purchase #5	$38.59	9.556%	$42.2777	$42.28	$42.30	$42.30
Purchase #6	$92.99	8.486%	$100.8811	$100.88	$100.90	$100.90
Purchase #7	$30.34	3.733%	$31.4726	$31.47	$31.45	$31.50
7 purchase totals =	$788.58		$846.5796	$846.58	$846.60	$846.60