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	$145.37	8.596%	$157.866	$157.87	$157.85	$157.90
Purchase #2	$143.88	7.644%	$154.8782	$154.88	$154.90	$154.90
Purchase #3	$133.79	8.323%	$144.9253	$144.93	$144.95	$144.90
Purchase #4	$165.67	7.664%	$178.3669	$178.37	$178.35	$178.40
Purchase #5	$80.94	10.588%	$89.5099	$89.51	$89.50	$89.50
Purchase #6	$74.93	7.862%	$80.821	$80.82	$80.80	$80.80
Purchase #7	$173.98	9.867%	$191.1466	$191.15	$191.15	$191.10
7 purchase totals =	$918.56		$997.5139	$997.53	$997.50	$997.50