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	$112.65	5.153%	$118.4549	$118.45	$118.45	$118.50
Purchase #2	$249.83	9.237%	$272.9068	$272.91	$272.90	$272.90
Purchase #3	$106.49	12.593%	$119.9003	$119.90	$119.90	$119.90
Purchase #4	$102.72	7.666%	$110.5945	$110.59	$110.60	$110.60
Purchase #5	$43.58	9.855%	$47.8748	$47.87	$47.85	$47.90
Purchase #6	$162.45	6.249%	$172.6015	$172.60	$172.60	$172.60
Purchase #7	$208.46	3.394%	$215.5351	$215.54	$215.55	$215.50
7 purchase totals =	$986.18		$1,057.8679	$1,057.86	$1,057.85	$1,057.90