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	$235.90	9.850%	$259.1362	$259.14	$259.15	$259.10
Purchase #2	$37.83	12.160%	$42.4301	$42.43	$42.45	$42.40
Purchase #3	$208.64	8.146%	$225.6358	$225.64	$225.65	$225.60
Purchase #4	$152.60	10.394%	$168.4612	$168.46	$168.45	$168.50
Purchase #5	$119.58	12.102%	$134.0516	$134.05	$134.05	$134.10
Purchase #6	$142.32	9.192%	$155.4021	$155.40	$155.40	$155.40
Purchase #7	$224.97	12.808%	$253.7842	$253.78	$253.80	$253.80
7 purchase totals =	$1,121.84		$1,238.9012	$1,238.90	$1,238.95	$1,238.90