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	$55.47	6.367%	$59.0018	$59.00	$59.00	$59.00
Purchase #2	$230.26	6.306%	$244.7802	$244.78	$244.80	$244.80
Purchase #3	$179.32	3.431%	$185.4725	$185.47	$185.45	$185.50
Purchase #4	$144.73	5.838%	$153.1793	$153.18	$153.20	$153.20
Purchase #5	$228.48	13.610%	$259.5761	$259.58	$259.60	$259.60
Purchase #6	$10.61	6.293%	$11.2777	$11.28	$11.30	$11.30
Purchase #7	$12.28	10.303%	$13.5452	$13.55	$13.55	$13.50
7 purchase totals =	$861.15		$926.8328	$926.84	$926.90	$926.90