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	$118.92	7.758%	$128.1458	$128.15	$128.15	$128.10
Purchase #2	$207.26	5.494%	$218.6469	$218.65	$218.65	$218.60
Purchase #3	$104.74	6.491%	$111.5387	$111.54	$111.55	$111.50
Purchase #4	$194.63	10.762%	$215.5761	$215.58	$215.60	$215.60
Purchase #5	$151.61	11.862%	$169.594	$169.59	$169.60	$169.60
Purchase #6	$69.46	13.440%	$78.7954	$78.80	$78.80	$78.80
Purchase #7	$53.86	4.585%	$56.3295	$56.33	$56.35	$56.30
7 purchase totals =	$900.48		$978.6264	$978.64	$978.70	$978.50