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	$83.83	7.279%	$89.932	$89.93	$89.95	$89.90
Purchase #2	$32.83	10.409%	$36.2473	$36.25	$36.25	$36.20
Purchase #3	$237.55	7.714%	$255.8746	$255.87	$255.85	$255.90
Purchase #4	$118.31	12.564%	$133.1745	$133.17	$133.15	$133.20
Purchase #5	$63.41	4.208%	$66.0783	$66.08	$66.10	$66.10
Purchase #6	$73.30	6.602%	$78.1393	$78.14	$78.15	$78.10
Purchase #7	$221.92	8.544%	$240.8808	$240.88	$240.90	$240.90
7 purchase totals =	$831.15		$900.3268	$900.32	$900.35	$900.30