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	$156.41	11.377%	$174.2048	$174.20	$174.20	$174.20
Purchase #2	$52.39	3.337%	$54.1383	$54.14	$54.15	$54.10
Purchase #3	$142.31	13.421%	$161.4094	$161.41	$161.40	$161.40
Purchase #4	$173.92	12.613%	$195.8565	$195.86	$195.85	$195.90
Purchase #5	$250.79	11.679%	$280.0798	$280.08	$280.10	$280.10
Purchase #6	$154.83	12.675%	$174.4547	$174.45	$174.45	$174.50
Purchase #7	$36.46	6.195%	$38.7187	$38.72	$38.70	$38.70
7 purchase totals =	$967.11		$1,078.8622	$1,078.86	$1,078.85	$1,078.90