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	$24.64	3.385%	$25.4741	$25.47	$25.45	$25.50
Purchase #2	$115.52	13.693%	$131.3382	$131.34	$131.35	$131.30
Purchase #3	$85.61	4.656%	$89.596	$89.60	$89.60	$89.60
Purchase #4	$70.43	10.626%	$77.9139	$77.91	$77.90	$77.90
Purchase #5	$105.98	13.724%	$120.5247	$120.52	$120.50	$120.50
Purchase #6	$87.68	9.312%	$95.8448	$95.84	$95.85	$95.80
Purchase #7	$31.60	5.242%	$33.2565	$33.26	$33.25	$33.30
7 purchase totals =	$521.46		$573.9482	$573.94	$573.90	$573.90