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	$155.57	10.289%	$171.5766	$171.58	$171.60	$171.60
Purchase #2	$204.97	10.863%	$227.2359	$227.24	$227.25	$227.20
Purchase #3	$87.86	7.361%	$94.3274	$94.33	$94.35	$94.30
Purchase #4	$90.92	11.668%	$101.5285	$101.53	$101.55	$101.50
Purchase #5	$137.61	10.162%	$151.5939	$151.59	$151.60	$151.60
Purchase #6	$108.95	13.775%	$123.9579	$123.96	$123.95	$124.00
Purchase #7	$48.59	12.613%	$54.7187	$54.72	$54.70	$54.70
7 purchase totals =	$834.47		$924.9389	$924.95	$925.00	$924.90