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	$105.57	10.417%	$116.5672	$116.57	$116.55	$116.60
Purchase #2	$107.94	6.595%	$115.0586	$115.06	$115.05	$115.10
Purchase #3	$218.85	13.175%	$247.6835	$247.68	$247.70	$247.70
Purchase #4	$142.59	9.832%	$156.6094	$156.61	$156.60	$156.60
Purchase #5	$57.84	6.248%	$61.4538	$61.45	$61.45	$61.50
Purchase #6	$16.93	8.192%	$18.3169	$18.32	$18.30	$18.30
Purchase #7	$99.55	5.747%	$105.2711	$105.27	$105.25	$105.30
7 purchase totals =	$749.27		$820.9605	$820.96	$820.90	$821.10