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	$117.32	11.808%	$131.1731	$131.17	$131.15	$131.20
Purchase #2	$38.66	12.329%	$43.4264	$43.43	$43.45	$43.40
Purchase #3	$198.60	3.809%	$206.1647	$206.16	$206.15	$206.20
Purchase #4	$179.45	13.142%	$203.0333	$203.03	$203.05	$203.00
Purchase #5	$117.96	11.789%	$131.8663	$131.87	$131.85	$131.90
Purchase #6	$169.86	6.206%	$180.4015	$180.40	$180.40	$180.40
Purchase #7	$183.60	10.645%	$203.1442	$203.14	$203.15	$203.10
7 purchase totals =	$1,005.45		$1,099.2095	$1,099.20	$1,099.20	$1,099.20