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	$80.86	12.137%	$90.674	$90.67	$90.65	$90.70
Purchase #2	$200.78	12.209%	$225.2932	$225.29	$225.30	$225.30
Purchase #3	$128.94	6.294%	$137.0555	$137.06	$137.05	$137.10
Purchase #4	$228.37	9.785%	$250.716	$250.72	$250.70	$250.70
Purchase #5	$76.69	13.380%	$86.9511	$86.95	$86.95	$87.00
Purchase #6	$230.76	9.296%	$252.2114	$252.21	$252.20	$252.20
Purchase #7	$250.45	5.620%	$264.5253	$264.53	$264.55	$264.50
7 purchase totals =	$1,196.85		$1,307.4265	$1,307.43	$1,307.40	$1,307.50