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	$25.41	7.768%	$27.3838	$27.38	$27.40	$27.40
Purchase #2	$208.72	7.500%	$224.374	$224.37	$224.35	$224.40
Purchase #3	$47.69	11.782%	$53.3088	$53.31	$53.30	$53.30
Purchase #4	$101.41	10.108%	$111.6605	$111.66	$111.65	$111.70
Purchase #5	$117.37	4.505%	$122.6575	$122.66	$122.65	$122.70
Purchase #6	$50.44	11.226%	$56.1024	$56.10	$56.10	$56.10
Purchase #7	$38.65	5.820%	$40.8994	$40.90	$40.90	$40.90
7 purchase totals =	$589.69		$636.3864	$636.38	$636.35	$636.50