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	$130.52	11.128%	$145.0443	$145.04	$145.05	$145.00
Purchase #2	$248.78	13.842%	$283.2161	$283.22	$283.20	$283.20
Purchase #3	$52.60	13.718%	$59.8157	$59.82	$59.80	$59.80
Purchase #4	$143.78	13.132%	$162.6612	$162.66	$162.65	$162.70
Purchase #5	$101.75	8.812%	$110.7162	$110.72	$110.70	$110.70
Purchase #6	$31.71	8.811%	$34.504	$34.50	$34.50	$34.50
Purchase #7	$170.27	7.103%	$182.3643	$182.36	$182.35	$182.40
7 purchase totals =	$879.41		$978.3218	$978.32	$978.25	$978.30