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	$158.56	12.308%	$178.0756	$178.08	$178.10	$178.10
Purchase #2	$71.50	9.527%	$78.3118	$78.31	$78.30	$78.30
Purchase #3	$131.42	3.837%	$136.4626	$136.46	$136.45	$136.50
Purchase #4	$12.94	13.234%	$14.6525	$14.65	$14.65	$14.70
Purchase #5	$77.64	10.747%	$85.984	$85.98	$86.00	$86.00
Purchase #6	$192.36	6.815%	$205.4693	$205.47	$205.45	$205.50
Purchase #7	$116.32	12.339%	$130.6727	$130.67	$130.65	$130.70
7 purchase totals =	$760.74		$829.6285	$829.62	$829.60	$829.80