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	$6.34	4.105%	$6.6003	$6.60	$6.60	$6.60
Purchase #2	$58.52	6.303%	$62.2085	$62.21	$62.20	$62.20
Purchase #3	$238.63	12.760%	$269.0792	$269.08	$269.10	$269.10
Purchase #4	$233.71	10.611%	$258.509	$258.51	$258.50	$258.50
Purchase #5	$17.31	5.468%	$18.2565	$18.26	$18.25	$18.30
Purchase #6	$122.64	12.410%	$137.8596	$137.86	$137.85	$137.90
Purchase #7	$233.82	12.582%	$263.2392	$263.24	$263.25	$263.20
7 purchase totals =	$910.97		$1,015.7523	$1,015.76	$1,015.75	$1,015.80