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	$45.73	10.677%	$50.6126	$50.61	$50.60	$50.60
Purchase #2	$145.76	4.752%	$152.6865	$152.69	$152.70	$152.70
Purchase #3	$202.53	5.686%	$214.0459	$214.05	$214.05	$214.00
Purchase #4	$43.46	8.874%	$47.3166	$47.32	$47.30	$47.30
Purchase #5	$19.37	5.270%	$20.3908	$20.39	$20.40	$20.40
Purchase #6	$42.85	5.724%	$45.3027	$45.30	$45.30	$45.30
Purchase #7	$249.73	12.239%	$280.2945	$280.29	$280.30	$280.30
7 purchase totals =	$749.43		$810.6496	$810.65	$810.65	$810.60