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	$103.28	6.370%	$109.8589	$109.86	$109.85	$109.90
Purchase #2	$233.40	10.737%	$258.4602	$258.46	$258.45	$258.50
Purchase #3	$24.35	12.667%	$27.4344	$27.43	$27.45	$27.40
Purchase #4	$69.80	5.771%	$73.8282	$73.83	$73.85	$73.80
Purchase #5	$104.37	6.782%	$111.4484	$111.45	$111.45	$111.40
Purchase #6	$83.65	9.727%	$91.7866	$91.79	$91.80	$91.80
Purchase #7	$94.41	11.778%	$105.5296	$105.53	$105.55	$105.50
7 purchase totals =	$713.26		$778.3463	$778.35	$778.40	$778.30