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	$53.56	11.819%	$59.8903	$59.89	$59.90	$59.90
Purchase #2	$13.84	12.239%	$15.5339	$15.53	$15.55	$15.50
Purchase #3	$234.55	5.866%	$248.3087	$248.31	$248.30	$248.30
Purchase #4	$36.95	8.796%	$40.2001	$40.20	$40.20	$40.20
Purchase #5	$17.96	5.283%	$18.9088	$18.91	$18.90	$18.90
Purchase #6	$87.42	9.161%	$95.4285	$95.43	$95.45	$95.40
Purchase #7	$243.94	6.376%	$259.4936	$259.49	$259.50	$259.50
7 purchase totals =	$688.22		$737.7639	$737.76	$737.80	$737.70