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	$86.42	3.867%	$89.7619	$89.76	$89.75	$89.80
Purchase #2	$202.69	6.108%	$215.0703	$215.07	$215.05	$215.10
Purchase #3	$27.77	12.762%	$31.314	$31.31	$31.30	$31.30
Purchase #4	$69.52	3.800%	$72.1618	$72.16	$72.15	$72.20
Purchase #5	$65.27	4.773%	$68.3853	$68.39	$68.40	$68.40
Purchase #6	$16.65	7.300%	$17.8655	$17.87	$17.85	$17.90
Purchase #7	$117.89	4.718%	$123.4521	$123.45	$123.45	$123.50
7 purchase totals =	$586.21		$618.0109	$618.01	$617.95	$618.20