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	$11.85	3.659%	$12.2836	$12.28	$12.30	$12.30
Purchase #2	$238.76	9.772%	$262.0916	$262.09	$262.10	$262.10
Purchase #3	$137.60	10.782%	$152.436	$152.44	$152.45	$152.40
Purchase #4	$36.53	12.498%	$41.0955	$41.10	$41.10	$41.10
Purchase #5	$134.59	7.167%	$144.2361	$144.24	$144.25	$144.20
Purchase #6	$145.67	8.726%	$158.3812	$158.38	$158.40	$158.40
Purchase #7	$29.76	4.528%	$31.1075	$31.11	$31.10	$31.10
7 purchase totals =	$734.76		$801.6315	$801.64	$801.70	$801.60