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	$27.89	3.727%	$28.9295	$28.93	$28.95	$28.90
Purchase #2	$177.35	4.370%	$185.1002	$185.10	$185.10	$185.10
Purchase #3	$179.97	10.536%	$198.9316	$198.93	$198.95	$198.90
Purchase #4	$109.55	5.744%	$115.8426	$115.84	$115.85	$115.80
Purchase #5	$111.62	9.189%	$121.8768	$121.88	$121.90	$121.90
Purchase #6	$212.31	4.840%	$222.5858	$222.59	$222.60	$222.60
Purchase #7	$109.96	12.648%	$123.8677	$123.87	$123.85	$123.90
7 purchase totals =	$928.65		$997.1342	$997.14	$997.20	$997.10