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	$59.73	10.109%	$65.7681	$65.77	$65.75	$65.80
Purchase #2	$69.80	7.730%	$75.1955	$75.20	$75.20	$75.20
Purchase #3	$52.99	12.158%	$59.4325	$59.43	$59.45	$59.40
Purchase #4	$161.50	6.201%	$171.5146	$171.51	$171.50	$171.50
Purchase #5	$121.79	4.834%	$127.6773	$127.68	$127.70	$127.70
Purchase #6	$16.84	4.564%	$17.6086	$17.61	$17.60	$17.60
Purchase #7	$68.96	4.602%	$72.1335	$72.13	$72.15	$72.10
7 purchase totals =	$551.61		$589.3301	$589.33	$589.35	$589.30