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	$241.58	12.559%	$271.92	$271.92	$271.90	$271.90
Purchase #2	$229.55	11.612%	$256.2053	$256.21	$256.20	$256.20
Purchase #3	$34.78	8.236%	$37.6445	$37.64	$37.65	$37.60
Purchase #4	$18.50	13.753%	$21.0443	$21.04	$21.05	$21.00
Purchase #5	$83.98	7.284%	$90.0971	$90.10	$90.10	$90.10
Purchase #6	$154.98	12.527%	$174.3943	$174.39	$174.40	$174.40
Purchase #7	$74.60	11.165%	$82.9291	$82.93	$82.95	$82.90
7 purchase totals =	$837.97		$934.2346	$934.23	$934.25	$934.10