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	$156.46	6.536%	$166.6862	$166.69	$166.70	$166.70
Purchase #2	$105.56	3.369%	$109.1163	$109.12	$109.10	$109.10
Purchase #3	$80.42	10.684%	$89.0121	$89.01	$89.00	$89.00
Purchase #4	$54.96	3.258%	$56.7506	$56.75	$56.75	$56.80
Purchase #5	$50.64	3.772%	$52.5501	$52.55	$52.55	$52.60
Purchase #6	$51.37	10.853%	$56.9452	$56.95	$56.95	$56.90
Purchase #7	$196.72	5.767%	$208.0648	$208.06	$208.05	$208.10
7 purchase totals =	$696.13		$739.1253	$739.13	$739.10	$739.20