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	$37.89	13.239%	$42.9063	$42.91	$42.90	$42.90
Purchase #2	$149.56	7.346%	$160.5467	$160.55	$160.55	$160.50
Purchase #3	$167.37	4.262%	$174.5033	$174.50	$174.50	$174.50
Purchase #4	$129.72	7.783%	$139.8161	$139.82	$139.80	$139.80
Purchase #5	$73.51	8.305%	$79.615	$79.62	$79.60	$79.60
Purchase #6	$173.49	6.838%	$185.3532	$185.35	$185.35	$185.40
Purchase #7	$149.31	5.693%	$157.8102	$157.81	$157.80	$157.80
7 purchase totals =	$880.85		$940.5508	$940.56	$940.50	$940.50