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	$214.71	3.147%	$221.4669	$221.47	$221.45	$221.50
Purchase #2	$148.80	10.431%	$164.3213	$164.32	$164.30	$164.30
Purchase #3	$67.85	5.869%	$71.8321	$71.83	$71.85	$71.80
Purchase #4	$183.74	11.712%	$205.2596	$205.26	$205.25	$205.30
Purchase #5	$235.61	11.538%	$262.7947	$262.79	$262.80	$262.80
Purchase #6	$53.82	3.161%	$55.5213	$55.52	$55.50	$55.50
Purchase #7	$9.25	11.675%	$10.3299	$10.33	$10.35	$10.30
7 purchase totals =	$913.78		$991.5258	$991.52	$991.50	$991.50