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	$34.94	10.579%	$38.6363	$38.64	$38.65	$38.60
Purchase #2	$246.93	12.832%	$278.6161	$278.62	$278.60	$278.60
Purchase #3	$236.99	5.206%	$249.3277	$249.33	$249.35	$249.30
Purchase #4	$198.52	6.831%	$212.0809	$212.08	$212.10	$212.10
Purchase #5	$79.50	4.323%	$82.9368	$82.94	$82.95	$82.90
Purchase #6	$71.72	9.440%	$78.4904	$78.49	$78.50	$78.50
Purchase #7	$31.28	3.783%	$32.4633	$32.46	$32.45	$32.50
7 purchase totals =	$899.88		$972.5515	$972.56	$972.60	$972.50