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	$70.76	8.666%	$76.8921	$76.89	$76.90	$76.90
Purchase #2	$138.46	10.432%	$152.9041	$152.90	$152.90	$152.90
Purchase #3	$50.39	13.666%	$57.2763	$57.28	$57.30	$57.30
Purchase #4	$78.30	5.588%	$82.6754	$82.68	$82.70	$82.70
Purchase #5	$99.59	4.431%	$104.0028	$104.00	$104.00	$104.00
Purchase #6	$97.86	8.786%	$106.458	$106.46	$106.45	$106.50
Purchase #7	$10.57	5.284%	$11.1285	$11.13	$11.15	$11.10
7 purchase totals =	$545.93		$591.3372	$591.34	$591.40	$591.40