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	$59.60	12.247%	$66.8992	$66.90	$66.90	$66.90
Purchase #2	$228.51	13.270%	$258.8333	$258.83	$258.85	$258.80
Purchase #3	$106.62	8.488%	$115.6699	$115.67	$115.65	$115.70
Purchase #4	$89.29	13.232%	$101.1049	$101.10	$101.10	$101.10
Purchase #5	$242.53	6.757%	$258.9178	$258.92	$258.90	$258.90
Purchase #6	$98.42	7.300%	$105.6047	$105.60	$105.60	$105.60
Purchase #7	$184.90	3.422%	$191.2273	$191.23	$191.25	$191.20
7 purchase totals =	$1,009.87		$1,098.2571	$1,098.25	$1,098.25	$1,098.20