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	$72.29	9.318%	$79.026	$79.03	$79.05	$79.00
Purchase #2	$91.45	9.577%	$100.2082	$100.21	$100.20	$100.20
Purchase #3	$76.61	6.524%	$81.608	$81.61	$81.60	$81.60
Purchase #4	$190.81	7.280%	$204.701	$204.70	$204.70	$204.70
Purchase #5	$150.32	9.654%	$164.8319	$164.83	$164.85	$164.80
Purchase #6	$77.64	10.186%	$85.5484	$85.55	$85.55	$85.50
Purchase #7	$234.88	11.854%	$262.7227	$262.72	$262.70	$262.70
7 purchase totals =	$894.00		$978.6462	$978.65	$978.65	$978.50