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	$89.42	11.636%	$99.8249	$99.82	$99.80	$99.80
Purchase #2	$119.78	12.643%	$134.9238	$134.92	$134.90	$134.90
Purchase #3	$228.87	3.809%	$237.5877	$237.59	$237.60	$237.60
Purchase #4	$237.85	7.430%	$255.5223	$255.52	$255.50	$255.50
Purchase #5	$18.75	3.343%	$19.3768	$19.38	$19.40	$19.40
Purchase #6	$81.25	7.529%	$87.3673	$87.37	$87.35	$87.40
Purchase #7	$243.36	6.205%	$258.4605	$258.46	$258.45	$258.50
7 purchase totals =	$1,019.28		$1,093.0633	$1,093.06	$1,093.00	$1,093.10