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	$84.85	5.737%	$89.7178	$89.72	$89.70	$89.70
Purchase #2	$35.29	7.609%	$37.9752	$37.98	$38.00	$38.00
Purchase #3	$199.99	6.286%	$212.5614	$212.56	$212.55	$212.60
Purchase #4	$60.38	11.546%	$67.3515	$67.35	$67.35	$67.40
Purchase #5	$105.70	3.628%	$109.5348	$109.53	$109.55	$109.50
Purchase #6	$197.85	8.434%	$214.5367	$214.54	$214.55	$214.50
Purchase #7	$169.83	12.189%	$190.5306	$190.53	$190.55	$190.50
7 purchase totals =	$853.89		$922.2080	$922.21	$922.25	$922.20