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	$238.51	7.497%	$256.3911	$256.39	$256.40	$256.40
Purchase #2	$117.80	9.147%	$128.5752	$128.58	$128.60	$128.60
Purchase #3	$62.86	13.250%	$71.189	$71.19	$71.20	$71.20
Purchase #4	$170.97	13.308%	$193.7227	$193.72	$193.70	$193.70
Purchase #5	$164.28	6.365%	$174.7364	$174.74	$174.75	$174.70
Purchase #6	$38.25	12.527%	$43.0416	$43.04	$43.05	$43.00
Purchase #7	$181.35	5.659%	$191.6126	$191.61	$191.60	$191.60
7 purchase totals =	$974.02		$1,059.2686	$1,059.27	$1,059.30	$1,059.20