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	$7.48	4.336%	$7.8043	$7.80	$7.80	$7.80
Purchase #2	$42.96	10.644%	$47.5327	$47.53	$47.55	$47.50
Purchase #3	$134.58	6.770%	$143.6911	$143.69	$143.70	$143.70
Purchase #4	$214.36	5.350%	$225.8283	$225.83	$225.85	$225.80
Purchase #5	$130.40	8.592%	$141.604	$141.60	$141.60	$141.60
Purchase #6	$164.34	13.127%	$185.9129	$185.91	$185.90	$185.90
Purchase #7	$201.77	4.604%	$211.0595	$211.06	$211.05	$211.10
7 purchase totals =	$895.89		$963.4328	$963.42	$963.45	$963.40