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	$9.39	10.816%	$10.4056	$10.41	$10.40	$10.40
Purchase #2	$144.96	9.257%	$158.3789	$158.38	$158.40	$158.40
Purchase #3	$223.47	3.214%	$230.6523	$230.65	$230.65	$230.70
Purchase #4	$117.89	10.337%	$130.0763	$130.08	$130.10	$130.10
Purchase #5	$76.42	3.151%	$78.828	$78.83	$78.85	$78.80
Purchase #6	$43.41	3.810%	$45.0639	$45.06	$45.05	$45.10
Purchase #7	$89.95	10.556%	$99.4451	$99.45	$99.45	$99.40
7 purchase totals =	$705.49		$752.8501	$752.86	$752.90	$752.90