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	$120.95	12.647%	$136.2465	$136.25	$136.25	$136.20
Purchase #2	$63.81	6.342%	$67.8568	$67.86	$67.85	$67.90
Purchase #3	$182.46	9.776%	$200.2973	$200.30	$200.30	$200.30
Purchase #4	$36.97	5.266%	$38.9168	$38.92	$38.90	$38.90
Purchase #5	$178.69	6.274%	$189.901	$189.90	$189.90	$189.90
Purchase #6	$111.37	13.604%	$126.5208	$126.52	$126.50	$126.50
Purchase #7	$43.55	3.839%	$45.2219	$45.22	$45.20	$45.20
7 purchase totals =	$737.80		$804.9611	$804.97	$804.90	$804.90