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	$88.35	13.747%	$100.4955	$100.50	$100.50	$100.50
Purchase #2	$67.94	11.858%	$75.9963	$76.00	$76.00	$76.00
Purchase #3	$133.55	3.443%	$138.1481	$138.15	$138.15	$138.10
Purchase #4	$65.35	10.759%	$72.381	$72.38	$72.40	$72.40
Purchase #5	$71.64	10.138%	$78.9029	$78.90	$78.90	$78.90
Purchase #6	$231.68	3.789%	$240.4584	$240.46	$240.45	$240.50
Purchase #7	$57.90	5.707%	$61.2044	$61.20	$61.20	$61.20
7 purchase totals =	$716.41		$767.5866	$767.59	$767.60	$767.60