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	$108.81	5.137%	$114.3996	$114.40	$114.40	$114.40
Purchase #2	$222.69	11.605%	$248.5332	$248.53	$248.55	$248.50
Purchase #3	$93.93	13.694%	$106.7928	$106.79	$106.80	$106.80
Purchase #4	$86.34	4.849%	$90.5266	$90.53	$90.55	$90.50
Purchase #5	$103.63	8.438%	$112.3743	$112.37	$112.35	$112.40
Purchase #6	$105.29	10.382%	$116.2212	$116.22	$116.20	$116.20
Purchase #7	$47.40	10.373%	$52.3168	$52.32	$52.30	$52.30
7 purchase totals =	$768.09		$841.1645	$841.16	$841.15	$841.10