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	$18.42	9.763%	$20.2183	$20.22	$20.20	$20.20
Purchase #2	$114.36	13.497%	$129.7952	$129.80	$129.80	$129.80
Purchase #3	$177.86	8.271%	$192.5708	$192.57	$192.55	$192.60
Purchase #4	$38.52	4.528%	$40.2642	$40.26	$40.25	$40.30
Purchase #5	$242.83	7.113%	$260.1025	$260.10	$260.10	$260.10
Purchase #6	$247.83	13.328%	$280.8608	$280.86	$280.85	$280.90
Purchase #7	$173.50	8.431%	$188.1278	$188.13	$188.15	$188.10
7 purchase totals =	$1,013.32		$1,111.9396	$1,111.94	$1,111.90	$1,112.00