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	$45.51	13.395%	$51.6061	$51.61	$51.60	$51.60
Purchase #2	$121.78	5.479%	$128.4523	$128.45	$128.45	$128.50
Purchase #3	$183.30	4.519%	$191.5833	$191.58	$191.60	$191.60
Purchase #4	$109.41	13.633%	$124.3259	$124.33	$124.35	$124.30
Purchase #5	$17.85	6.552%	$19.0195	$19.02	$19.00	$19.00
Purchase #6	$243.81	9.743%	$267.5644	$267.56	$267.55	$267.60
Purchase #7	$186.53	5.125%	$196.0897	$196.09	$196.10	$196.10
7 purchase totals =	$908.19		$978.6412	$978.64	$978.65	$978.70