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	$65.68	6.751%	$70.1141	$70.11	$70.10	$70.10
Purchase #2	$169.44	13.487%	$192.2924	$192.29	$192.30	$192.30
Purchase #3	$234.83	11.660%	$262.2112	$262.21	$262.20	$262.20
Purchase #4	$143.59	4.507%	$150.0616	$150.06	$150.05	$150.10
Purchase #5	$154.43	13.248%	$174.8889	$174.89	$174.90	$174.90
Purchase #6	$123.49	10.642%	$136.6318	$136.63	$136.65	$136.60
Purchase #7	$28.87	11.478%	$32.1837	$32.18	$32.20	$32.20
7 purchase totals =	$920.33		$1,018.3837	$1,018.37	$1,018.40	$1,018.40