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	$78.39	4.730%	$82.0978	$82.10	$82.10	$82.10
Purchase #2	$243.58	11.586%	$271.8012	$271.80	$271.80	$271.80
Purchase #3	$78.93	12.190%	$88.5516	$88.55	$88.55	$88.60
Purchase #4	$145.57	9.192%	$158.9508	$158.95	$158.95	$159.00
Purchase #5	$128.56	3.217%	$132.6958	$132.70	$132.70	$132.70
Purchase #6	$38.91	12.304%	$43.6975	$43.70	$43.70	$43.70
Purchase #7	$9.67	10.773%	$10.7117	$10.71	$10.70	$10.70
7 purchase totals =	$723.61		$788.5064	$788.51	$788.50	$788.60