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	$89.39	10.145%	$98.4586	$98.46	$98.45	$98.50
Purchase #2	$144.64	13.644%	$164.3747	$164.37	$164.35	$164.40
Purchase #3	$210.25	9.455%	$230.1291	$230.13	$230.15	$230.10
Purchase #4	$174.96	7.136%	$187.4451	$187.45	$187.45	$187.40
Purchase #5	$115.43	10.367%	$127.3966	$127.40	$127.40	$127.40
Purchase #6	$52.92	11.257%	$58.8772	$58.88	$58.90	$58.90
Purchase #7	$166.91	3.543%	$172.8236	$172.82	$172.80	$172.80
7 purchase totals =	$954.50		$1,039.5049	$1,039.51	$1,039.50	$1,039.50