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	$34.90	6.639%	$37.217	$37.22	$37.20	$37.20
Purchase #2	$97.94	13.289%	$110.9552	$110.96	$110.95	$111.00
Purchase #3	$199.27	13.721%	$226.6118	$226.61	$226.60	$226.60
Purchase #4	$45.43	13.504%	$51.5649	$51.56	$51.55	$51.60
Purchase #5	$202.30	8.440%	$219.3741	$219.37	$219.35	$219.40
Purchase #6	$214.64	3.547%	$222.2533	$222.25	$222.25	$222.30
Purchase #7	$106.82	4.718%	$111.8598	$111.86	$111.85	$111.90
7 purchase totals =	$901.30		$979.8361	$979.83	$979.75	$980.00