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	$95.72	4.485%	$100.013	$100.01	$100.00	$100.00
Purchase #2	$101.40	9.481%	$111.0137	$111.01	$111.00	$111.00
Purchase #3	$99.99	5.797%	$105.7864	$105.79	$105.80	$105.80
Purchase #4	$154.38	11.358%	$171.9145	$171.91	$171.90	$171.90
Purchase #5	$133.27	13.761%	$151.6093	$151.61	$151.60	$151.60
Purchase #6	$108.54	9.758%	$119.1313	$119.13	$119.15	$119.10
Purchase #7	$120.77	3.352%	$124.8182	$124.82	$124.80	$124.80
7 purchase totals =	$814.07		$884.2864	$884.28	$884.25	$884.20