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	$150.48	4.666%	$157.5014	$157.50	$157.50	$157.50
Purchase #2	$39.99	13.569%	$45.4162	$45.42	$45.40	$45.40
Purchase #3	$37.68	8.711%	$40.9623	$40.96	$40.95	$41.00
Purchase #4	$227.59	6.233%	$241.7757	$241.78	$241.80	$241.80
Purchase #5	$137.82	5.393%	$145.2526	$145.25	$145.25	$145.30
Purchase #6	$178.58	3.697%	$185.1821	$185.18	$185.20	$185.20
Purchase #7	$38.77	10.323%	$42.7722	$42.77	$42.75	$42.80
7 purchase totals =	$810.91		$858.8625	$858.86	$858.85	$859.00