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	$100.84	10.226%	$111.1519	$111.15	$111.15	$111.20
Purchase #2	$120.65	8.793%	$131.2588	$131.26	$131.25	$131.30
Purchase #3	$200.65	11.717%	$224.1602	$224.16	$224.15	$224.20
Purchase #4	$62.94	5.713%	$66.5358	$66.54	$66.55	$66.50
Purchase #5	$40.50	6.659%	$43.1969	$43.20	$43.20	$43.20
Purchase #6	$119.40	8.807%	$129.9156	$129.92	$129.90	$129.90
Purchase #7	$132.59	9.506%	$145.194	$145.19	$145.20	$145.20
7 purchase totals =	$777.57		$851.4132	$851.42	$851.40	$851.50