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	$81.85	10.151%	$90.1586	$90.16	$90.15	$90.20
Purchase #2	$115.33	11.459%	$128.5457	$128.55	$128.55	$128.50
Purchase #3	$115.99	3.527%	$120.081	$120.08	$120.10	$120.10
Purchase #4	$97.65	6.573%	$104.0685	$104.07	$104.05	$104.10
Purchase #5	$95.47	8.871%	$103.9391	$103.94	$103.95	$103.90
Purchase #6	$37.65	13.329%	$42.6684	$42.67	$42.65	$42.70
Purchase #7	$206.65	9.162%	$225.5833	$225.58	$225.60	$225.60
7 purchase totals =	$750.59		$815.0446	$815.05	$815.05	$815.10