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	$23.95	11.720%	$26.7569	$26.76	$26.75	$26.80
Purchase #2	$69.45	4.665%	$72.6898	$72.69	$72.70	$72.70
Purchase #3	$164.82	5.499%	$173.8835	$173.88	$173.90	$173.90
Purchase #4	$40.39	5.489%	$42.607	$42.61	$42.60	$42.60
Purchase #5	$69.55	12.752%	$78.419	$78.42	$78.40	$78.40
Purchase #6	$208.58	9.236%	$227.8444	$227.84	$227.85	$227.80
Purchase #7	$202.45	8.289%	$219.2311	$219.23	$219.25	$219.20
7 purchase totals =	$779.19		$841.4317	$841.43	$841.45	$841.40