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	$120.69	5.661%	$127.5223	$127.52	$127.50	$127.50
Purchase #2	$136.84	13.571%	$155.4106	$155.41	$155.40	$155.40
Purchase #3	$97.69	12.482%	$109.8837	$109.88	$109.90	$109.90
Purchase #4	$54.55	9.842%	$59.9188	$59.92	$59.90	$59.90
Purchase #5	$230.43	4.574%	$240.9699	$240.97	$240.95	$241.00
Purchase #6	$172.25	4.628%	$180.2217	$180.22	$180.20	$180.20
Purchase #7	$66.72	11.130%	$74.1459	$74.15	$74.15	$74.10
7 purchase totals =	$879.17		$948.0729	$948.07	$948.00	$948.00