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	$193.48	12.399%	$217.4696	$217.47	$217.45	$217.50
Purchase #2	$109.94	6.689%	$117.2939	$117.29	$117.30	$117.30
Purchase #3	$76.89	7.188%	$82.4169	$82.42	$82.40	$82.40
Purchase #4	$164.59	3.305%	$170.0297	$170.03	$170.05	$170.00
Purchase #5	$166.52	8.788%	$181.1538	$181.15	$181.15	$181.20
Purchase #6	$104.96	13.264%	$118.8819	$118.88	$118.90	$118.90
Purchase #7	$134.32	12.855%	$151.5868	$151.59	$151.60	$151.60
7 purchase totals =	$950.70		$1,038.8326	$1,038.83	$1,038.85	$1,038.90