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	$146.77	12.154%	$164.6084	$164.61	$164.60	$164.60
Purchase #2	$123.65	6.109%	$131.2038	$131.20	$131.20	$131.20
Purchase #3	$231.57	4.503%	$241.9976	$242.00	$242.00	$242.00
Purchase #4	$128.72	9.546%	$141.0076	$141.01	$141.00	$141.00
Purchase #5	$205.27	7.738%	$221.1538	$221.15	$221.15	$221.20
Purchase #6	$169.88	7.488%	$182.6006	$182.60	$182.60	$182.60
Purchase #7	$58.59	4.265%	$61.0889	$61.09	$61.10	$61.10
7 purchase totals =	$1,064.45		$1,143.6607	$1,143.66	$1,143.65	$1,143.70