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	$131.94	9.602%	$144.6089	$144.61	$144.60	$144.60
Purchase #2	$49.32	8.452%	$53.4885	$53.49	$53.50	$53.50
Purchase #3	$154.35	6.438%	$164.2871	$164.29	$164.30	$164.30
Purchase #4	$136.62	6.796%	$145.9047	$145.90	$145.90	$145.90
Purchase #5	$73.76	10.822%	$81.7423	$81.74	$81.75	$81.70
Purchase #6	$58.97	4.272%	$61.4892	$61.49	$61.50	$61.50
Purchase #7	$55.39	4.542%	$57.9058	$57.91	$57.90	$57.90
7 purchase totals =	$660.35		$709.4265	$709.43	$709.45	$709.40