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	$119.83	5.604%	$126.5453	$126.55	$126.55	$126.50
Purchase #2	$178.88	12.154%	$200.6211	$200.62	$200.60	$200.60
Purchase #3	$61.85	6.623%	$65.9463	$65.95	$65.95	$65.90
Purchase #4	$195.30	10.573%	$215.9491	$215.95	$215.95	$215.90
Purchase #5	$66.26	6.803%	$70.7677	$70.77	$70.75	$70.80
Purchase #6	$104.82	7.839%	$113.0368	$113.04	$113.05	$113.00
Purchase #7	$159.40	3.174%	$164.4594	$164.46	$164.45	$164.50
7 purchase totals =	$886.34		$957.3257	$957.34	$957.30	$957.20