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	$179.87	7.441%	$193.2541	$193.25	$193.25	$193.30
Purchase #2	$133.47	5.556%	$140.8856	$140.89	$140.90	$140.90
Purchase #3	$229.82	12.357%	$258.2189	$258.22	$258.20	$258.20
Purchase #4	$122.54	6.540%	$130.5541	$130.55	$130.55	$130.60
Purchase #5	$219.83	4.570%	$229.8762	$229.88	$229.90	$229.90
Purchase #6	$38.53	13.547%	$43.7497	$43.75	$43.75	$43.70
Purchase #7	$10.92	8.321%	$11.8287	$11.83	$11.85	$11.80
7 purchase totals =	$934.98		$1,008.3673	$1,008.37	$1,008.40	$1,008.40