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	$250.47	5.132%	$263.3241	$263.32	$263.30	$263.30
Purchase #2	$87.72	3.563%	$90.8455	$90.85	$90.85	$90.80
Purchase #3	$155.70	9.833%	$171.01	$171.01	$171.00	$171.00
Purchase #4	$186.70	7.413%	$200.5401	$200.54	$200.55	$200.50
Purchase #5	$188.90	5.548%	$199.3802	$199.38	$199.40	$199.40
Purchase #6	$124.89	10.798%	$138.3756	$138.38	$138.40	$138.40
Purchase #7	$15.28	11.862%	$17.0925	$17.09	$17.10	$17.10
7 purchase totals =	$1,009.66		$1,080.5680	$1,080.57	$1,080.60	$1,080.50