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	$36.54	7.736%	$39.3667	$39.37	$39.35	$39.40
Purchase #2	$213.93	6.335%	$227.4825	$227.48	$227.50	$227.50
Purchase #3	$76.71	12.340%	$86.176	$86.18	$86.20	$86.20
Purchase #4	$138.39	9.277%	$151.2284	$151.23	$151.25	$151.20
Purchase #5	$150.38	10.712%	$166.4887	$166.49	$166.50	$166.50
Purchase #6	$183.97	7.827%	$198.3693	$198.37	$198.35	$198.40
Purchase #7	$151.40	11.723%	$169.1486	$169.15	$169.15	$169.10
7 purchase totals =	$951.32		$1,038.2602	$1,038.27	$1,038.30	$1,038.30