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	$120.41	9.219%	$131.5106	$131.51	$131.50	$131.50
Purchase #2	$233.40	10.604%	$258.1497	$258.15	$258.15	$258.10
Purchase #3	$106.91	11.130%	$118.8091	$118.81	$118.80	$118.80
Purchase #4	$71.42	9.233%	$78.0142	$78.01	$78.00	$78.00
Purchase #5	$8.75	9.195%	$9.5546	$9.55	$9.55	$9.60
Purchase #6	$144.51	6.849%	$154.4075	$154.41	$154.40	$154.40
Purchase #7	$130.63	12.628%	$147.126	$147.13	$147.15	$147.10
7 purchase totals =	$816.03		$897.5717	$897.57	$897.55	$897.50