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	$81.96	9.203%	$89.5028	$89.50	$89.50	$89.50
Purchase #2	$117.53	12.473%	$132.1895	$132.19	$132.20	$132.20
Purchase #3	$110.31	5.853%	$116.7664	$116.77	$116.75	$116.80
Purchase #4	$40.84	6.628%	$43.5469	$43.55	$43.55	$43.50
Purchase #5	$204.31	8.240%	$221.1451	$221.15	$221.15	$221.10
Purchase #6	$157.62	13.457%	$178.8309	$178.83	$178.85	$178.80
Purchase #7	$223.46	3.293%	$230.8185	$230.82	$230.80	$230.80
7 purchase totals =	$936.03		$1,012.8001	$1,012.81	$1,012.80	$1,012.70