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	$231.47	3.418%	$239.3816	$239.38	$239.40	$239.40
Purchase #2	$54.89	7.451%	$58.9799	$58.98	$59.00	$59.00
Purchase #3	$208.72	9.633%	$228.826	$228.83	$228.85	$228.80
Purchase #4	$162.88	6.303%	$173.1463	$173.15	$173.15	$173.10
Purchase #5	$35.52	13.673%	$40.3766	$40.38	$40.40	$40.40
Purchase #6	$100.92	8.463%	$109.4609	$109.46	$109.45	$109.50
Purchase #7	$6.88	5.180%	$7.2364	$7.24	$7.25	$7.20
7 purchase totals =	$801.28		$857.4077	$857.42	$857.50	$857.40