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	$63.52	7.534%	$68.3056	$68.31	$68.30	$68.30
Purchase #2	$40.68	10.619%	$44.9998	$45.00	$45.00	$45.00
Purchase #3	$153.56	11.654%	$171.4559	$171.46	$171.45	$171.50
Purchase #4	$189.59	5.730%	$200.4535	$200.45	$200.45	$200.50
Purchase #5	$43.67	7.724%	$47.0431	$47.04	$47.05	$47.00
Purchase #6	$240.64	12.175%	$269.9379	$269.94	$269.95	$269.90
Purchase #7	$87.96	12.696%	$99.1274	$99.13	$99.15	$99.10
7 purchase totals =	$819.62		$901.3232	$901.33	$901.35	$901.30