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	$38.59	5.578%	$40.7426	$40.74	$40.75	$40.70
Purchase #2	$169.82	9.731%	$186.3452	$186.35	$186.35	$186.30
Purchase #3	$250.31	5.400%	$263.8267	$263.83	$263.85	$263.80
Purchase #4	$148.59	8.359%	$161.0106	$161.01	$161.00	$161.00
Purchase #5	$72.55	12.383%	$81.5339	$81.53	$81.55	$81.50
Purchase #6	$87.29	9.655%	$95.7178	$95.72	$95.70	$95.70
Purchase #7	$227.93	12.727%	$256.9387	$256.94	$256.95	$256.90
7 purchase totals =	$995.08		$1,086.1155	$1,086.12	$1,086.15	$1,085.90