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	$34.99	13.202%	$39.6094	$39.61	$39.60	$39.60
Purchase #2	$158.75	5.714%	$167.821	$167.82	$167.80	$167.80
Purchase #3	$240.60	9.119%	$262.5403	$262.54	$262.55	$262.50
Purchase #4	$104.69	4.429%	$109.3267	$109.33	$109.35	$109.30
Purchase #5	$178.53	9.121%	$194.8137	$194.81	$194.80	$194.80
Purchase #6	$213.65	9.677%	$234.3249	$234.32	$234.30	$234.30
Purchase #7	$83.44	5.810%	$88.2879	$88.29	$88.30	$88.30
7 purchase totals =	$1,014.65		$1,096.7239	$1,096.72	$1,096.70	$1,096.60