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	$99.91	7.659%	$107.5621	$107.56	$107.55	$107.60
Purchase #2	$209.72	9.608%	$229.8699	$229.87	$229.85	$229.90
Purchase #3	$203.82	7.606%	$219.3225	$219.32	$219.30	$219.30
Purchase #4	$116.43	9.325%	$127.2871	$127.29	$127.30	$127.30
Purchase #5	$196.35	3.323%	$202.8747	$202.87	$202.85	$202.90
Purchase #6	$39.77	3.500%	$41.162	$41.16	$41.15	$41.20
Purchase #7	$124.83	11.819%	$139.5837	$139.58	$139.60	$139.60
7 purchase totals =	$990.83		$1,067.6620	$1,067.65	$1,067.60	$1,067.80