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	$108.45	7.218%	$116.2779	$116.28	$116.30	$116.30
Purchase #2	$172.46	8.290%	$186.7569	$186.76	$186.75	$186.80
Purchase #3	$134.31	11.719%	$150.0498	$150.05	$150.05	$150.00
Purchase #4	$215.38	5.827%	$227.9302	$227.93	$227.95	$227.90
Purchase #5	$17.65	9.222%	$19.2777	$19.28	$19.30	$19.30
Purchase #6	$104.99	6.380%	$111.6884	$111.69	$111.70	$111.70
Purchase #7	$192.78	5.706%	$203.78	$203.78	$203.80	$203.80
7 purchase totals =	$946.02		$1,015.7609	$1,015.77	$1,015.85	$1,015.80