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	$40.78	12.532%	$45.8905	$45.89	$45.90	$45.90
Purchase #2	$160.53	4.236%	$167.3301	$167.33	$167.35	$167.30
Purchase #3	$158.37	10.782%	$175.4455	$175.45	$175.45	$175.40
Purchase #4	$196.70	7.522%	$211.4958	$211.50	$211.50	$211.50
Purchase #5	$220.32	10.847%	$244.2181	$244.22	$244.20	$244.20
Purchase #6	$177.93	9.368%	$194.5985	$194.60	$194.60	$194.60
Purchase #7	$101.42	11.127%	$112.705	$112.71	$112.70	$112.70
7 purchase totals =	$1,056.05		$1,151.6835	$1,151.70	$1,151.70	$1,151.60