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	$101.25	10.488%	$111.8691	$111.87	$111.85	$111.90
Purchase #2	$85.87	5.838%	$90.8831	$90.88	$90.90	$90.90
Purchase #3	$76.39	9.453%	$83.6111	$83.61	$83.60	$83.60
Purchase #4	$198.25	11.686%	$221.4175	$221.42	$221.40	$221.40
Purchase #5	$206.26	13.836%	$234.7981	$234.80	$234.80	$234.80
Purchase #6	$37.43	7.624%	$40.2837	$40.28	$40.30	$40.30
Purchase #7	$12.81	5.640%	$13.5325	$13.53	$13.55	$13.50
7 purchase totals =	$718.26		$796.3951	$796.39	$796.40	$796.40