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	$238.42	9.554%	$261.1986	$261.20	$261.20	$261.20
Purchase #2	$228.29	11.358%	$254.2192	$254.22	$254.20	$254.20
Purchase #3	$157.44	6.569%	$167.7822	$167.78	$167.80	$167.80
Purchase #4	$221.36	7.752%	$238.5198	$238.52	$238.50	$238.50
Purchase #5	$29.63	11.106%	$32.9207	$32.92	$32.90	$32.90
Purchase #6	$127.31	9.484%	$139.3841	$139.38	$139.40	$139.40
Purchase #7	$80.56	5.575%	$85.0512	$85.05	$85.05	$85.10
7 purchase totals =	$1,083.01		$1,179.0758	$1,179.07	$1,179.05	$1,179.10