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	$40.46	7.461%	$43.4787	$43.48	$43.50	$43.50
Purchase #2	$123.41	13.786%	$140.4233	$140.42	$140.40	$140.40
Purchase #3	$185.38	10.838%	$205.4715	$205.47	$205.45	$205.50
Purchase #4	$76.67	4.213%	$79.9001	$79.90	$79.90	$79.90
Purchase #5	$156.95	6.122%	$166.5585	$166.56	$166.55	$166.60
Purchase #6	$187.67	5.834%	$198.6187	$198.62	$198.60	$198.60
Purchase #7	$185.35	4.645%	$193.9595	$193.96	$193.95	$194.00
7 purchase totals =	$955.89		$1,028.4103	$1,028.41	$1,028.35	$1,028.50