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	$147.84	11.479%	$164.8106	$164.81	$164.80	$164.80
Purchase #2	$241.38	6.420%	$256.8766	$256.88	$256.90	$256.90
Purchase #3	$7.54	5.536%	$7.9574	$7.96	$7.95	$8.00
Purchase #4	$111.78	13.724%	$127.1207	$127.12	$127.10	$127.10
Purchase #5	$143.36	4.857%	$150.323	$150.32	$150.30	$150.30
Purchase #6	$43.61	5.737%	$46.1119	$46.11	$46.10	$46.10
Purchase #7	$123.38	5.236%	$129.8402	$129.84	$129.85	$129.80
7 purchase totals =	$818.89		$883.0404	$883.04	$883.00	$883.00