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	$9.95	11.212%	$11.0656	$11.07	$11.05	$11.10
Purchase #2	$164.68	13.141%	$186.3206	$186.32	$186.30	$186.30
Purchase #3	$16.38	10.728%	$18.1372	$18.14	$18.15	$18.10
Purchase #4	$140.57	13.830%	$160.0108	$160.01	$160.00	$160.00
Purchase #5	$150.56	3.459%	$155.7679	$155.77	$155.75	$155.80
Purchase #6	$100.93	10.291%	$111.3167	$111.32	$111.30	$111.30
Purchase #7	$12.59	7.632%	$13.5509	$13.55	$13.55	$13.60
7 purchase totals =	$595.66		$656.1697	$656.18	$656.10	$656.20