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	$239.25	6.757%	$255.4161	$255.42	$255.40	$255.40
Purchase #2	$13.79	9.285%	$15.0704	$15.07	$15.05	$15.10
Purchase #3	$164.30	13.823%	$187.0112	$187.01	$187.00	$187.00
Purchase #4	$101.77	7.553%	$109.4567	$109.46	$109.45	$109.50
Purchase #5	$234.92	11.376%	$261.6445	$261.64	$261.65	$261.60
Purchase #6	$191.30	11.635%	$213.5578	$213.56	$213.55	$213.60
Purchase #7	$113.81	4.150%	$118.5331	$118.53	$118.55	$118.50
7 purchase totals =	$1,059.14		$1,160.6898	$1,160.69	$1,160.65	$1,160.70