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	$134.90	11.845%	$150.8789	$150.88	$150.90	$150.90
Purchase #2	$51.83	9.184%	$56.5901	$56.59	$56.60	$56.60
Purchase #3	$221.79	5.828%	$234.7159	$234.72	$234.70	$234.70
Purchase #4	$243.61	5.746%	$257.6078	$257.61	$257.60	$257.60
Purchase #5	$53.93	6.785%	$57.5892	$57.59	$57.60	$57.60
Purchase #6	$61.52	11.363%	$68.5105	$68.51	$68.50	$68.50
Purchase #7	$139.94	3.833%	$145.3039	$145.30	$145.30	$145.30
7 purchase totals =	$907.52		$971.1963	$971.20	$971.20	$971.20