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	$120.69	9.307%	$131.9226	$131.92	$131.90	$131.90
Purchase #2	$112.89	12.492%	$126.9922	$126.99	$127.00	$127.00
Purchase #3	$244.92	13.125%	$277.0658	$277.07	$277.05	$277.10
Purchase #4	$78.39	5.291%	$82.5376	$82.54	$82.55	$82.50
Purchase #5	$115.46	12.225%	$129.575	$129.58	$129.60	$129.60
Purchase #6	$195.82	9.694%	$214.8028	$214.80	$214.80	$214.80
Purchase #7	$140.61	10.664%	$155.6047	$155.60	$155.60	$155.60
7 purchase totals =	$1,008.78		$1,118.5007	$1,118.50	$1,118.50	$1,118.50