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	$238.60	11.485%	$266.0032	$266.00	$266.00	$266.00
Purchase #2	$13.63	13.131%	$15.4198	$15.42	$15.40	$15.40
Purchase #3	$144.62	9.262%	$158.0147	$158.01	$158.00	$158.00
Purchase #4	$40.56	3.506%	$41.982	$41.98	$42.00	$42.00
Purchase #5	$215.38	7.385%	$231.2858	$231.29	$231.30	$231.30
Purchase #6	$30.78	9.576%	$33.7275	$33.73	$33.75	$33.70
Purchase #7	$68.58	5.767%	$72.535	$72.54	$72.55	$72.50
7 purchase totals =	$752.15		$818.9680	$818.97	$819.00	$818.90