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	$173.58	9.368%	$189.841	$189.84	$189.85	$189.80
Purchase #2	$76.30	11.372%	$84.9768	$84.98	$85.00	$85.00
Purchase #3	$78.28	10.270%	$86.3194	$86.32	$86.30	$86.30
Purchase #4	$50.70	7.838%	$54.6739	$54.67	$54.65	$54.70
Purchase #5	$97.43	3.117%	$100.4669	$100.47	$100.45	$100.50
Purchase #6	$48.68	10.696%	$53.8868	$53.89	$53.90	$53.90
Purchase #7	$64.67	6.482%	$68.8619	$68.86	$68.85	$68.90
7 purchase totals =	$589.64		$639.0267	$639.03	$639.00	$639.10