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	$193.37	10.766%	$214.1882	$214.19	$214.20	$214.20
Purchase #2	$40.27	13.262%	$45.6106	$45.61	$45.60	$45.60
Purchase #3	$40.25	6.841%	$43.0035	$43.00	$43.00	$43.00
Purchase #4	$89.36	11.484%	$99.6221	$99.62	$99.60	$99.60
Purchase #5	$63.46	12.207%	$71.2066	$71.21	$71.20	$71.20
Purchase #6	$78.31	5.617%	$82.7087	$82.71	$82.70	$82.70
Purchase #7	$92.35	12.464%	$103.8605	$103.86	$103.85	$103.90
7 purchase totals =	$597.37		$660.2002	$660.20	$660.15	$660.20