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	$105.78	9.570%	$115.9031	$115.90	$115.90	$115.90
Purchase #2	$87.25	11.346%	$97.1494	$97.15	$97.15	$97.10
Purchase #3	$50.75	9.298%	$55.4687	$55.47	$55.45	$55.50
Purchase #4	$229.76	4.396%	$239.8602	$239.86	$239.85	$239.90
Purchase #5	$228.79	5.345%	$241.0188	$241.02	$241.00	$241.00
Purchase #6	$49.98	7.808%	$53.8824	$53.88	$53.90	$53.90
Purchase #7	$177.82	10.408%	$196.3275	$196.33	$196.35	$196.30
7 purchase totals =	$930.13		$999.6101	$999.61	$999.60	$999.60