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	$242.79	5.185%	$255.3787	$255.38	$255.40	$255.40
Purchase #2	$164.57	10.786%	$182.3205	$182.32	$182.30	$182.30
Purchase #3	$182.54	9.695%	$200.2373	$200.24	$200.25	$200.20
Purchase #4	$51.40	3.631%	$53.2663	$53.27	$53.25	$53.30
Purchase #5	$24.39	12.458%	$27.4285	$27.43	$27.45	$27.40
Purchase #6	$55.98	12.627%	$63.0486	$63.05	$63.05	$63.00
Purchase #7	$153.95	5.833%	$162.9299	$162.93	$162.95	$162.90
7 purchase totals =	$875.62		$944.6098	$944.62	$944.65	$944.50