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	$53.71	5.867%	$56.8612	$56.86	$56.85	$56.90
Purchase #2	$217.67	10.656%	$240.8649	$240.86	$240.85	$240.90
Purchase #3	$66.49	7.634%	$71.5658	$71.57	$71.55	$71.60
Purchase #4	$163.61	13.520%	$185.7301	$185.73	$185.75	$185.70
Purchase #5	$97.51	12.360%	$109.5622	$109.56	$109.55	$109.60
Purchase #6	$41.30	4.500%	$43.1585	$43.16	$43.15	$43.20
Purchase #7	$242.96	7.482%	$261.1383	$261.14	$261.15	$261.10
7 purchase totals =	$883.25		$968.8810	$968.88	$968.85	$969.00