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	$244.67	10.721%	$270.9011	$270.90	$270.90	$270.90
Purchase #2	$59.96	9.328%	$65.5531	$65.55	$65.55	$65.60
Purchase #3	$39.48	13.533%	$44.8228	$44.82	$44.80	$44.80
Purchase #4	$170.55	11.421%	$190.0285	$190.03	$190.05	$190.00
Purchase #5	$127.27	5.724%	$134.5549	$134.55	$134.55	$134.60
Purchase #6	$83.30	8.305%	$90.2181	$90.22	$90.20	$90.20
Purchase #7	$235.80	6.788%	$251.8061	$251.81	$251.80	$251.80
7 purchase totals =	$961.03		$1,047.8846	$1,047.88	$1,047.85	$1,047.90