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	$27.97	11.236%	$31.1127	$31.11	$31.10	$31.10
Purchase #2	$206.70	11.402%	$230.2679	$230.27	$230.25	$230.30
Purchase #3	$152.32	11.299%	$169.5306	$169.53	$169.55	$169.50
Purchase #4	$101.96	5.406%	$107.472	$107.47	$107.45	$107.50
Purchase #5	$153.70	11.362%	$171.1634	$171.16	$171.15	$171.20
Purchase #6	$210.94	9.722%	$231.4476	$231.45	$231.45	$231.40
Purchase #7	$118.91	7.598%	$127.9448	$127.94	$127.95	$127.90
7 purchase totals =	$972.50		$1,068.9390	$1,068.93	$1,068.90	$1,068.90