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	$18.40	8.634%	$19.9887	$19.99	$20.00	$20.00
Purchase #2	$76.81	7.864%	$82.8503	$82.85	$82.85	$82.90
Purchase #3	$125.37	11.336%	$139.5819	$139.58	$139.60	$139.60
Purchase #4	$200.43	5.160%	$210.7722	$210.77	$210.75	$210.80
Purchase #5	$78.82	8.870%	$85.8113	$85.81	$85.80	$85.80
Purchase #6	$181.29	8.229%	$196.2084	$196.21	$196.20	$196.20
Purchase #7	$84.95	13.423%	$96.3528	$96.35	$96.35	$96.40
7 purchase totals =	$766.07		$831.5656	$831.56	$831.55	$831.70