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	$118.58	5.220%	$124.7699	$124.77	$124.75	$124.80
Purchase #2	$101.50	9.768%	$111.4145	$111.41	$111.40	$111.40
Purchase #3	$226.98	5.568%	$239.6182	$239.62	$239.60	$239.60
Purchase #4	$116.65	3.165%	$120.342	$120.34	$120.35	$120.30
Purchase #5	$222.53	12.105%	$249.4673	$249.47	$249.45	$249.50
Purchase #6	$20.25	6.142%	$21.4938	$21.49	$21.50	$21.50
Purchase #7	$131.64	12.845%	$148.5492	$148.55	$148.55	$148.50
7 purchase totals =	$938.13		$1,015.6549	$1,015.65	$1,015.60	$1,015.60