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	$227.47	3.208%	$234.7672	$234.77	$234.75	$234.80
Purchase #2	$78.87	8.751%	$85.7719	$85.77	$85.75	$85.80
Purchase #3	$220.27	6.484%	$234.5523	$234.55	$234.55	$234.60
Purchase #4	$237.90	6.201%	$252.6522	$252.65	$252.65	$252.70
Purchase #5	$100.99	10.221%	$111.3122	$111.31	$111.30	$111.30
Purchase #6	$60.77	10.681%	$67.2608	$67.26	$67.25	$67.30
Purchase #7	$134.71	12.481%	$151.5232	$151.52	$151.50	$151.50
7 purchase totals =	$1,060.98		$1,137.8398	$1,137.83	$1,137.75	$1,138.00