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	$224.37	9.418%	$245.5012	$245.50	$245.50	$245.50
Purchase #2	$104.68	13.744%	$119.0672	$119.07	$119.05	$119.10
Purchase #3	$57.56	3.658%	$59.6655	$59.67	$59.65	$59.70
Purchase #4	$43.93	3.580%	$45.5027	$45.50	$45.50	$45.50
Purchase #5	$141.85	5.762%	$150.0234	$150.02	$150.00	$150.00
Purchase #6	$95.56	3.266%	$98.681	$98.68	$98.70	$98.70
Purchase #7	$53.89	10.319%	$59.4509	$59.45	$59.45	$59.50
7 purchase totals =	$721.84		$777.8919	$777.89	$777.85	$778.00