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	$81.59	9.169%	$89.071	$89.07	$89.05	$89.10
Purchase #2	$167.81	4.451%	$175.2792	$175.28	$175.30	$175.30
Purchase #3	$175.79	13.606%	$199.708	$199.71	$199.70	$199.70
Purchase #4	$214.99	4.714%	$225.1246	$225.12	$225.10	$225.10
Purchase #5	$12.37	10.685%	$13.6917	$13.69	$13.70	$13.70
Purchase #6	$137.86	13.533%	$156.5166	$156.52	$156.50	$156.50
Purchase #7	$194.89	13.123%	$220.4654	$220.47	$220.45	$220.50
7 purchase totals =	$985.30		$1,079.8565	$1,079.86	$1,079.80	$1,079.90