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	$54.28	6.316%	$57.7083	$57.71	$57.70	$57.70
Purchase #2	$113.49	12.755%	$127.9656	$127.97	$127.95	$128.00
Purchase #3	$207.51	4.493%	$216.8334	$216.83	$216.85	$216.80
Purchase #4	$234.39	6.660%	$250.0004	$250.00	$250.00	$250.00
Purchase #5	$165.38	12.422%	$185.9235	$185.92	$185.90	$185.90
Purchase #6	$185.36	10.532%	$204.8821	$204.88	$204.90	$204.90
Purchase #7	$200.56	9.500%	$219.6132	$219.61	$219.60	$219.60
7 purchase totals =	$1,160.97		$1,262.9265	$1,262.92	$1,262.90	$1,262.90