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	$54.58	5.678%	$57.6791	$57.68	$57.70	$57.70
Purchase #2	$237.61	4.848%	$249.1293	$249.13	$249.15	$249.10
Purchase #3	$11.85	13.382%	$13.4358	$13.44	$13.45	$13.40
Purchase #4	$243.44	7.116%	$260.7632	$260.76	$260.75	$260.80
Purchase #5	$78.71	13.486%	$89.3248	$89.32	$89.30	$89.30
Purchase #6	$107.98	10.487%	$119.3039	$119.30	$119.30	$119.30
Purchase #7	$83.93	6.756%	$89.6003	$89.60	$89.60	$89.60
7 purchase totals =	$818.10		$879.2364	$879.23	$879.25	$879.20