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	$153.40	12.168%	$172.0657	$172.07	$172.05	$172.10
Purchase #2	$50.26	12.370%	$56.4772	$56.48	$56.50	$56.50
Purchase #3	$5.46	8.180%	$5.9066	$5.91	$5.90	$5.90
Purchase #4	$205.81	10.558%	$227.5394	$227.54	$227.55	$227.50
Purchase #5	$77.29	13.180%	$87.4768	$87.48	$87.50	$87.50
Purchase #6	$233.68	11.745%	$261.1257	$261.13	$261.15	$261.10
Purchase #7	$86.34	3.571%	$89.4232	$89.42	$89.40	$89.40
7 purchase totals =	$812.24		$900.0146	$900.03	$900.05	$900.00