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	$6.78	11.492%	$7.5592	$7.56	$7.55	$7.60
Purchase #2	$188.72	6.194%	$200.4093	$200.41	$200.40	$200.40
Purchase #3	$67.49	7.366%	$72.4613	$72.46	$72.45	$72.50
Purchase #4	$44.91	11.631%	$50.1335	$50.13	$50.15	$50.10
Purchase #5	$164.60	12.395%	$185.0022	$185.00	$185.00	$185.00
Purchase #6	$48.37	3.512%	$50.0688	$50.07	$50.05	$50.10
Purchase #7	$161.26	13.727%	$183.3962	$183.40	$183.40	$183.40
7 purchase totals =	$682.13		$749.0305	$749.03	$749.00	$749.10