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	$29.34	13.541%	$33.3129	$33.31	$33.30	$33.30
Purchase #2	$107.92	5.109%	$113.4336	$113.43	$113.45	$113.40
Purchase #3	$38.58	4.853%	$40.4523	$40.45	$40.45	$40.50
Purchase #4	$14.52	9.340%	$15.8762	$15.88	$15.90	$15.90
Purchase #5	$110.29	3.531%	$114.1843	$114.18	$114.20	$114.20
Purchase #6	$107.83	3.730%	$111.8521	$111.85	$111.85	$111.90
Purchase #7	$211.83	13.172%	$239.7322	$239.73	$239.75	$239.70
7 purchase totals =	$620.31		$668.8436	$668.83	$668.90	$668.90