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	$83.65	3.756%	$86.7919	$86.79	$86.80	$86.80
Purchase #2	$128.68	13.670%	$146.2706	$146.27	$146.25	$146.30
Purchase #3	$13.43	8.143%	$14.5236	$14.52	$14.50	$14.50
Purchase #4	$167.29	9.184%	$182.6539	$182.65	$182.65	$182.70
Purchase #5	$194.37	10.127%	$214.0538	$214.05	$214.05	$214.10
Purchase #6	$242.60	13.621%	$275.6445	$275.64	$275.65	$275.60
Purchase #7	$150.76	12.410%	$169.4693	$169.47	$169.45	$169.50
7 purchase totals =	$980.78		$1,089.4076	$1,089.39	$1,089.35	$1,089.50