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	$75.97	3.771%	$78.8348	$78.83	$78.85	$78.80
Purchase #2	$64.59	10.298%	$71.2415	$71.24	$71.25	$71.20
Purchase #3	$181.57	9.440%	$198.7102	$198.71	$198.70	$198.70
Purchase #4	$186.69	12.516%	$210.0561	$210.06	$210.05	$210.10
Purchase #5	$209.37	10.222%	$230.7718	$230.77	$230.75	$230.80
Purchase #6	$17.55	3.615%	$18.1844	$18.18	$18.20	$18.20
Purchase #7	$50.87	3.262%	$52.5294	$52.53	$52.55	$52.50
7 purchase totals =	$786.61		$860.3282	$860.32	$860.35	$860.30