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	$175.54	5.724%	$185.5879	$185.59	$185.60	$185.60
Purchase #2	$105.38	7.855%	$113.6576	$113.66	$113.65	$113.70
Purchase #3	$173.69	7.400%	$186.5431	$186.54	$186.55	$186.50
Purchase #4	$124.83	5.224%	$131.3511	$131.35	$131.35	$131.40
Purchase #5	$65.44	7.124%	$70.1019	$70.10	$70.10	$70.10
Purchase #6	$35.27	4.562%	$36.879	$36.88	$36.90	$36.90
Purchase #7	$164.72	11.849%	$184.2377	$184.24	$184.25	$184.20
7 purchase totals =	$844.87		$908.3583	$908.36	$908.40	$908.40