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	$242.71	11.170%	$269.8207	$269.82	$269.80	$269.80
Purchase #2	$30.89	12.734%	$34.8235	$34.82	$34.80	$34.80
Purchase #3	$39.77	6.705%	$42.4366	$42.44	$42.45	$42.40
Purchase #4	$17.88	13.773%	$20.3426	$20.34	$20.35	$20.30
Purchase #5	$56.55	5.456%	$59.6354	$59.64	$59.65	$59.60
Purchase #6	$183.50	6.296%	$195.0532	$195.05	$195.05	$195.10
Purchase #7	$45.28	11.530%	$50.5008	$50.50	$50.50	$50.50
7 purchase totals =	$616.58		$672.6128	$672.61	$672.60	$672.50