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	$50.79	8.139%	$54.9238	$54.92	$54.90	$54.90
Purchase #2	$121.37	10.556%	$134.1818	$134.18	$134.20	$134.20
Purchase #3	$107.36	3.536%	$111.1562	$111.16	$111.15	$111.20
Purchase #4	$109.93	13.340%	$124.5947	$124.59	$124.60	$124.60
Purchase #5	$180.87	9.528%	$198.1033	$198.10	$198.10	$198.10
Purchase #6	$132.70	13.571%	$150.7087	$150.71	$150.70	$150.70
Purchase #7	$73.75	11.238%	$82.038	$82.04	$82.05	$82.00
7 purchase totals =	$776.77		$855.7065	$855.70	$855.70	$855.70