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	$89.54	3.773%	$92.9183	$92.92	$92.90	$92.90
Purchase #2	$27.66	3.602%	$28.6563	$28.66	$28.65	$28.70
Purchase #3	$10.72	5.464%	$11.3057	$11.31	$11.30	$11.30
Purchase #4	$197.58	4.139%	$205.7578	$205.76	$205.75	$205.80
Purchase #5	$75.79	10.592%	$83.8177	$83.82	$83.80	$83.80
Purchase #6	$97.45	3.425%	$100.7877	$100.79	$100.80	$100.80
Purchase #7	$104.76	10.694%	$115.963	$115.96	$115.95	$116.00
7 purchase totals =	$603.50		$639.2065	$639.22	$639.15	$639.30