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	$156.44	10.266%	$172.5001	$172.50	$172.50	$172.50
Purchase #2	$76.93	9.483%	$84.2253	$84.23	$84.25	$84.20
Purchase #3	$10.99	12.541%	$12.3683	$12.37	$12.35	$12.40
Purchase #4	$78.86	8.818%	$85.8139	$85.81	$85.80	$85.80
Purchase #5	$55.60	4.222%	$57.9474	$57.95	$57.95	$57.90
Purchase #6	$78.81	13.854%	$89.7283	$89.73	$89.75	$89.70
Purchase #7	$101.73	6.147%	$107.9833	$107.98	$108.00	$108.00
7 purchase totals =	$559.36		$610.5666	$610.57	$610.60	$610.50