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	$115.32	11.477%	$128.5553	$128.56	$128.55	$128.60
Purchase #2	$120.66	12.341%	$135.5507	$135.55	$135.55	$135.60
Purchase #3	$38.79	9.587%	$42.5088	$42.51	$42.50	$42.50
Purchase #4	$179.78	3.128%	$185.4035	$185.40	$185.40	$185.40
Purchase #5	$162.87	5.776%	$172.2774	$172.28	$172.30	$172.30
Purchase #6	$13.38	10.493%	$14.784	$14.78	$14.80	$14.80
Purchase #7	$95.58	7.156%	$102.4197	$102.42	$102.40	$102.40
7 purchase totals =	$726.38		$781.4994	$781.50	$781.50	$781.60