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	$142.87	12.420%	$160.6145	$160.61	$160.60	$160.60
Purchase #2	$59.27	13.866%	$67.4884	$67.49	$67.50	$67.50
Purchase #3	$220.93	3.333%	$228.2936	$228.29	$228.30	$228.30
Purchase #4	$109.56	8.132%	$118.4694	$118.47	$118.45	$118.50
Purchase #5	$77.57	8.460%	$84.1324	$84.13	$84.15	$84.10
Purchase #6	$103.82	5.480%	$109.5093	$109.51	$109.50	$109.50
Purchase #7	$88.57	7.370%	$95.0976	$95.10	$95.10	$95.10
7 purchase totals =	$802.59		$863.6052	$863.60	$863.60	$863.60