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	$99.78	8.583%	$108.3441	$108.34	$108.35	$108.30
Purchase #2	$213.49	6.340%	$227.0253	$227.03	$227.05	$227.00
Purchase #3	$117.77	3.214%	$121.5551	$121.56	$121.55	$121.60
Purchase #4	$98.81	12.662%	$111.3213	$111.32	$111.30	$111.30
Purchase #5	$69.33	10.222%	$76.4169	$76.42	$76.40	$76.40
Purchase #6	$67.40	7.305%	$72.3236	$72.32	$72.30	$72.30
Purchase #7	$19.55	7.841%	$21.0829	$21.08	$21.10	$21.10
7 purchase totals =	$686.13		$738.0692	$738.07	$738.05	$738.00